| Message ID | 1343442065-15646-4-git-send-email-asias@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 07/28/2012 04:21 AM, Asias He wrote: > This patch introduces bio-based IO path for virtio-blk. > > Compared to request-based IO path, bio-based IO path uses driver > provided ->make_request_fn() method to bypasses the IO scheduler. It > handles the bio to device directly without allocating a request in block > layer. This reduces the IO path in guest kernel to achieve high IOPS > and lower latency. The downside is that guest can not use the IO > scheduler to merge and sort requests. However, this is not a big problem > if the backend disk in host side uses faster disk device. > > When the bio-based IO path is not enabled, virtio-blk still uses the > original request-based IO path, no performance difference is observed. > > Performance evaluation: > ----------------------------- > 1) Fio test is performed in a 8 vcpu guest with ramdisk based guest using > kvm tool. > > Short version: > With bio-based IO path, sequential read/write, random read/write > IOPS boost : 28%, 24%, 21%, 16% > Latency improvement: 32%, 17%, 21%, 16% > > Long version: > With bio-based IO path: > seq-read : io=2048.0MB, bw=116996KB/s, iops=233991 , runt= 17925msec > seq-write : io=2048.0MB, bw=100829KB/s, iops=201658 , runt= 20799msec > rand-read : io=3095.7MB, bw=112134KB/s, iops=224268 , runt= 28269msec > rand-write: io=3095.7MB, bw=96198KB/s, iops=192396 , runt= 32952msec > clat (usec): min=0 , max=2631.6K, avg=58716.99, stdev=191377.30 > clat (usec): min=0 , max=1753.2K, avg=66423.25, stdev=81774.35 > clat (usec): min=0 , max=2915.5K, avg=61685.70, stdev=120598.39 > clat (usec): min=0 , max=1933.4K, avg=76935.12, stdev=96603.45 > cpu : usr=74.08%, sys=703.84%, ctx=29661403, majf=21354, minf=22460954 > cpu : usr=70.92%, sys=702.81%, ctx=77219828, majf=13980, minf=27713137 > cpu : usr=72.23%, sys=695.37%, ctx=88081059, majf=18475, minf=28177648 > cpu : usr=69.69%, sys=654.13%, ctx=145476035, majf=15867, minf=26176375 > With request-based IO path: > seq-read : io=2048.0MB, bw=91074KB/s, iops=182147 , runt= 23027msec > seq-write : io=2048.0MB, bw=80725KB/s, iops=161449 , runt= 25979msec > rand-read : io=3095.7MB, bw=92106KB/s, iops=184211 , runt= 34416msec > rand-write: io=3095.7MB, bw=82815KB/s, iops=165630 , runt= 38277msec > clat (usec): min=0 , max=1932.4K, avg=77824.17, stdev=170339.49 > clat (usec): min=0 , max=2510.2K, avg=78023.96, stdev=146949.15 > clat (usec): min=0 , max=3037.2K, avg=74746.53, stdev=128498.27 > clat (usec): min=0 , max=1363.4K, avg=89830.75, stdev=114279.68 > cpu : usr=53.28%, sys=724.19%, ctx=37988895, majf=17531, minf=23577622 > cpu : usr=49.03%, sys=633.20%, ctx=205935380, majf=18197, minf=27288959 > cpu : usr=55.78%, sys=722.40%, ctx=101525058, majf=19273, minf=28067082 > cpu : usr=56.55%, sys=690.83%, ctx=228205022, majf=18039, minf=26551985 > > 2) Fio test is performed in a 8 vcpu guest with Fusion-IO based guest using > kvm tool. > > Short version: > With bio-based IO path, sequential read/write, random read/write > IOPS boost : 11%, 11%, 13%, 10% > Latency improvement: 10%, 10%, 12%, 10% > Long Version: > With bio-based IO path: > read : io=2048.0MB, bw=58920KB/s, iops=117840 , runt= 35593msec > write: io=2048.0MB, bw=64308KB/s, iops=128616 , runt= 32611msec > read : io=3095.7MB, bw=59633KB/s, iops=119266 , runt= 53157msec > write: io=3095.7MB, bw=62993KB/s, iops=125985 , runt= 50322msec > clat (usec): min=0 , max=1284.3K, avg=128109.01, stdev=71513.29 > clat (usec): min=94 , max=962339 , avg=116832.95, stdev=65836.80 > clat (usec): min=0 , max=1846.6K, avg=128509.99, stdev=89575.07 > clat (usec): min=0 , max=2256.4K, avg=121361.84, stdev=82747.25 > cpu : usr=56.79%, sys=421.70%, ctx=147335118, majf=21080, minf=19852517 > cpu : usr=61.81%, sys=455.53%, ctx=143269950, majf=16027, minf=24800604 > cpu : usr=63.10%, sys=455.38%, ctx=178373538, majf=16958, minf=24822612 > cpu : usr=62.04%, sys=453.58%, ctx=226902362, majf=16089, minf=23278105 > With request-based IO path: > read : io=2048.0MB, bw=52896KB/s, iops=105791 , runt= 39647msec > write: io=2048.0MB, bw=57856KB/s, iops=115711 , runt= 36248msec > read : io=3095.7MB, bw=52387KB/s, iops=104773 , runt= 60510msec > write: io=3095.7MB, bw=57310KB/s, iops=114619 , runt= 55312msec > clat (usec): min=0 , max=1532.6K, avg=142085.62, stdev=109196.84 > clat (usec): min=0 , max=1487.4K, avg=129110.71, stdev=114973.64 > clat (usec): min=0 , max=1388.6K, avg=145049.22, stdev=107232.55 > clat (usec): min=0 , max=1465.9K, avg=133585.67, stdev=110322.95 > cpu : usr=44.08%, sys=590.71%, ctx=451812322, majf=14841, minf=17648641 > cpu : usr=48.73%, sys=610.78%, ctx=418953997, majf=22164, minf=26850689 > cpu : usr=45.58%, sys=581.16%, ctx=714079216, majf=21497, minf=22558223 > cpu : usr=48.40%, sys=599.65%, ctx=656089423, majf=16393, minf=23824409 What are the cases where we'll see a performance degradation with using the bio path? Could we measure performance for those as well? > How to use: > ----------------------------- > Add 'virtio_blk.use_bio=1' to kernel cmdline or 'modprobe virtio_blk > use_bio=1' to enable ->make_request_fn() based I/O path. If there are, in fact, no cases where performance is degraded, can use_bio=1 be the default? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sat, Jul 28, 2012 at 10:21:05AM +0800, Asias He wrote: > This patch introduces bio-based IO path for virtio-blk. > > Compared to request-based IO path, bio-based IO path uses driver > provided ->make_request_fn() method to bypasses the IO scheduler. It > handles the bio to device directly without allocating a request in block > layer. This reduces the IO path in guest kernel to achieve high IOPS > and lower latency. The downside is that guest can not use the IO > scheduler to merge and sort requests. However, this is not a big problem > if the backend disk in host side uses faster disk device. If this optimization depends on the host, then it should be reported to the guest using a feature bit, as opposed to being guest driven. > When the bio-based IO path is not enabled, virtio-blk still uses the > original request-based IO path, no performance difference is observed. > > Performance evaluation: > ----------------------------- > 1) Fio test is performed in a 8 vcpu guest with ramdisk based guest using > kvm tool. > > Short version: > With bio-based IO path, sequential read/write, random read/write > IOPS boost : 28%, 24%, 21%, 16% > Latency improvement: 32%, 17%, 21%, 16% > > Long version: > With bio-based IO path: > seq-read : io=2048.0MB, bw=116996KB/s, iops=233991 , runt= 17925msec > seq-write : io=2048.0MB, bw=100829KB/s, iops=201658 , runt= 20799msec > rand-read : io=3095.7MB, bw=112134KB/s, iops=224268 , runt= 28269msec > rand-write: io=3095.7MB, bw=96198KB/s, iops=192396 , runt= 32952msec > clat (usec): min=0 , max=2631.6K, avg=58716.99, stdev=191377.30 > clat (usec): min=0 , max=1753.2K, avg=66423.25, stdev=81774.35 > clat (usec): min=0 , max=2915.5K, avg=61685.70, stdev=120598.39 > clat (usec): min=0 , max=1933.4K, avg=76935.12, stdev=96603.45 > cpu : usr=74.08%, sys=703.84%, ctx=29661403, majf=21354, minf=22460954 > cpu : usr=70.92%, sys=702.81%, ctx=77219828, majf=13980, minf=27713137 > cpu : usr=72.23%, sys=695.37%, ctx=88081059, majf=18475, minf=28177648 > cpu : usr=69.69%, sys=654.13%, ctx=145476035, majf=15867, minf=26176375 > With request-based IO path: > seq-read : io=2048.0MB, bw=91074KB/s, iops=182147 , runt= 23027msec > seq-write : io=2048.0MB, bw=80725KB/s, iops=161449 , runt= 25979msec > rand-read : io=3095.7MB, bw=92106KB/s, iops=184211 , runt= 34416msec > rand-write: io=3095.7MB, bw=82815KB/s, iops=165630 , runt= 38277msec > clat (usec): min=0 , max=1932.4K, avg=77824.17, stdev=170339.49 > clat (usec): min=0 , max=2510.2K, avg=78023.96, stdev=146949.15 > clat (usec): min=0 , max=3037.2K, avg=74746.53, stdev=128498.27 > clat (usec): min=0 , max=1363.4K, avg=89830.75, stdev=114279.68 > cpu : usr=53.28%, sys=724.19%, ctx=37988895, majf=17531, minf=23577622 > cpu : usr=49.03%, sys=633.20%, ctx=205935380, majf=18197, minf=27288959 > cpu : usr=55.78%, sys=722.40%, ctx=101525058, majf=19273, minf=28067082 > cpu : usr=56.55%, sys=690.83%, ctx=228205022, majf=18039, minf=26551985 So bio based causes cpu to jump up by some 30%? What happens if you divide IOPS/CPU? Any improvement that comes from increasing the cpu share of the given guest on the host will not scale well on a typical overcommitted host. > 2) Fio test is performed in a 8 vcpu guest with Fusion-IO based guest using > kvm tool. > > Short version: > With bio-based IO path, sequential read/write, random read/write > IOPS boost : 11%, 11%, 13%, 10% > Latency improvement: 10%, 10%, 12%, 10% > Long Version: > With bio-based IO path: > read : io=2048.0MB, bw=58920KB/s, iops=117840 , runt= 35593msec > write: io=2048.0MB, bw=64308KB/s, iops=128616 , runt= 32611msec > read : io=3095.7MB, bw=59633KB/s, iops=119266 , runt= 53157msec > write: io=3095.7MB, bw=62993KB/s, iops=125985 , runt= 50322msec > clat (usec): min=0 , max=1284.3K, avg=128109.01, stdev=71513.29 > clat (usec): min=94 , max=962339 , avg=116832.95, stdev=65836.80 > clat (usec): min=0 , max=1846.6K, avg=128509.99, stdev=89575.07 > clat (usec): min=0 , max=2256.4K, avg=121361.84, stdev=82747.25 > cpu : usr=56.79%, sys=421.70%, ctx=147335118, majf=21080, minf=19852517 > cpu : usr=61.81%, sys=455.53%, ctx=143269950, majf=16027, minf=24800604 > cpu : usr=63.10%, sys=455.38%, ctx=178373538, majf=16958, minf=24822612 > cpu : usr=62.04%, sys=453.58%, ctx=226902362, majf=16089, minf=23278105 > With request-based IO path: > read : io=2048.0MB, bw=52896KB/s, iops=105791 , runt= 39647msec > write: io=2048.0MB, bw=57856KB/s, iops=115711 , runt= 36248msec > read : io=3095.7MB, bw=52387KB/s, iops=104773 , runt= 60510msec > write: io=3095.7MB, bw=57310KB/s, iops=114619 , runt= 55312msec > clat (usec): min=0 , max=1532.6K, avg=142085.62, stdev=109196.84 > clat (usec): min=0 , max=1487.4K, avg=129110.71, stdev=114973.64 > clat (usec): min=0 , max=1388.6K, avg=145049.22, stdev=107232.55 > clat (usec): min=0 , max=1465.9K, avg=133585.67, stdev=110322.95 > cpu : usr=44.08%, sys=590.71%, ctx=451812322, majf=14841, minf=17648641 > cpu : usr=48.73%, sys=610.78%, ctx=418953997, majf=22164, minf=26850689 > cpu : usr=45.58%, sys=581.16%, ctx=714079216, majf=21497, minf=22558223 > cpu : usr=48.40%, sys=599.65%, ctx=656089423, majf=16393, minf=23824409 Is this host or guest cpu? We should probably measure host cpu as this includes device overhead which could vary by load. > How to use: > ----------------------------- > Add 'virtio_blk.use_bio=1' to kernel cmdline or 'modprobe virtio_blk > use_bio=1' to enable ->make_request_fn() based I/O path. > > Cc: Rusty Russell <rusty@rustcorp.com.au> > Cc: "Michael S. Tsirkin" <mst@redhat.com> > Cc: virtualization@lists.linux-foundation.org > Cc: kvm@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Acked-by: Rusty Russell <rusty@rustcorp.com.au> > Signed-off-by: Christoph Hellwig <hch@lst.de> > Signed-off-by: Minchan Kim <minchan.kim@gmail.com> > Signed-off-by: Asias He <asias@redhat.com> > --- > drivers/block/virtio_blk.c | 203 +++++++++++++++++++++++++++++++++++--------- > 1 file changed, 163 insertions(+), 40 deletions(-) > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > index c0bbeb4..95cfeed 100644 > --- a/drivers/block/virtio_blk.c > +++ b/drivers/block/virtio_blk.c > @@ -14,6 +14,9 @@ > > #define PART_BITS 4 > > +static bool use_bio; > +module_param(use_bio, bool, S_IRUGO); > + > static int major; > static DEFINE_IDA(vd_index_ida); > > @@ -23,6 +26,7 @@ struct virtio_blk > { > struct virtio_device *vdev; > struct virtqueue *vq; > + wait_queue_head_t queue_wait; > > /* The disk structure for the kernel. */ > struct gendisk *disk; > @@ -51,53 +55,87 @@ struct virtio_blk > struct virtblk_req > { > struct request *req; > + struct bio *bio; > struct virtio_blk_outhdr out_hdr; > struct virtio_scsi_inhdr in_hdr; > u8 status; > + struct scatterlist sg[]; > }; > > -static void blk_done(struct virtqueue *vq) > +static inline int virtblk_result(struct virtblk_req *vbr) > +{ > + switch (vbr->status) { > + case VIRTIO_BLK_S_OK: > + return 0; > + case VIRTIO_BLK_S_UNSUPP: > + return -ENOTTY; > + default: > + return -EIO; > + } > +} > + > +static inline void virtblk_request_done(struct virtio_blk *vblk, > + struct virtblk_req *vbr) > +{ > + struct request *req = vbr->req; > + int error = virtblk_result(vbr); > + > + if (req->cmd_type == REQ_TYPE_BLOCK_PC) { > + req->resid_len = vbr->in_hdr.residual; > + req->sense_len = vbr->in_hdr.sense_len; > + req->errors = vbr->in_hdr.errors; > + } else if (req->cmd_type == REQ_TYPE_SPECIAL) { > + req->errors = (error != 0); > + } > + > + __blk_end_request_all(req, error); > + mempool_free(vbr, vblk->pool); > +} > + > +static inline void virtblk_bio_done(struct virtio_blk *vblk, > + struct virtblk_req *vbr) > +{ > + bio_endio(vbr->bio, virtblk_result(vbr)); > + mempool_free(vbr, vblk->pool); > +} > + > +static void virtblk_done(struct virtqueue *vq) > { > struct virtio_blk *vblk = vq->vdev->priv; > + unsigned long bio_done = 0, req_done = 0; > struct virtblk_req *vbr; > - unsigned int len; > unsigned long flags; > + unsigned int len; > > spin_lock_irqsave(vblk->disk->queue->queue_lock, flags); > while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) { > - int error; > - > - switch (vbr->status) { > - case VIRTIO_BLK_S_OK: > - error = 0; > - break; > - case VIRTIO_BLK_S_UNSUPP: > - error = -ENOTTY; > - break; > - default: > - error = -EIO; > - break; > - } > - > - switch (vbr->req->cmd_type) { > - case REQ_TYPE_BLOCK_PC: > - vbr->req->resid_len = vbr->in_hdr.residual; > - vbr->req->sense_len = vbr->in_hdr.sense_len; > - vbr->req->errors = vbr->in_hdr.errors; > - break; > - case REQ_TYPE_SPECIAL: > - vbr->req->errors = (error != 0); > - break; > - default: > - break; > + if (vbr->bio) { > + virtblk_bio_done(vblk, vbr); > + bio_done++; > + } else { > + virtblk_request_done(vblk, vbr); > + req_done++; > } > - > - __blk_end_request_all(vbr->req, error); > - mempool_free(vbr, vblk->pool); > } > /* In case queue is stopped waiting for more buffers. */ > - blk_start_queue(vblk->disk->queue); > + if (req_done) > + blk_start_queue(vblk->disk->queue); > spin_unlock_irqrestore(vblk->disk->queue->queue_lock, flags); > + > + if (bio_done) > + wake_up(&vblk->queue_wait); > +} > + > +static inline struct virtblk_req *virtblk_alloc_req(struct virtio_blk *vblk, > + gfp_t gfp_mask) > +{ > + struct virtblk_req *vbr; > + > + vbr = mempool_alloc(vblk->pool, gfp_mask); > + if (vbr && use_bio) > + sg_init_table(vbr->sg, vblk->sg_elems); > + > + return vbr; > } > > static bool do_req(struct request_queue *q, struct virtio_blk *vblk, > @@ -106,13 +144,13 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, > unsigned long num, out = 0, in = 0; > struct virtblk_req *vbr; > > - vbr = mempool_alloc(vblk->pool, GFP_ATOMIC); > + vbr = virtblk_alloc_req(vblk, GFP_ATOMIC); > if (!vbr) > /* When another request finishes we'll try again. */ > return false; > > vbr->req = req; > - > + vbr->bio = NULL; > if (req->cmd_flags & REQ_FLUSH) { > vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH; > vbr->out_hdr.sector = 0; > @@ -172,7 +210,8 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, > } > } > > - if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr, GFP_ATOMIC)<0) { > + if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr, > + GFP_ATOMIC) < 0) { > mempool_free(vbr, vblk->pool); > return false; > } > @@ -180,7 +219,7 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, > return true; > } > > -static void do_virtblk_request(struct request_queue *q) > +static void virtblk_request(struct request_queue *q) > { > struct virtio_blk *vblk = q->queuedata; > struct request *req; > @@ -203,6 +242,82 @@ static void do_virtblk_request(struct request_queue *q) > virtqueue_kick(vblk->vq); > } > > +static void virtblk_add_buf_wait(struct virtio_blk *vblk, > + struct virtblk_req *vbr, > + unsigned long out, > + unsigned long in) > +{ > + DEFINE_WAIT(wait); > + > + for (;;) { > + prepare_to_wait_exclusive(&vblk->queue_wait, &wait, > + TASK_UNINTERRUPTIBLE); > + > + spin_lock_irq(vblk->disk->queue->queue_lock); > + if (virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr, > + GFP_ATOMIC) < 0) { > + spin_unlock_irq(vblk->disk->queue->queue_lock); > + io_schedule(); > + } else { > + virtqueue_kick(vblk->vq); > + spin_unlock_irq(vblk->disk->queue->queue_lock); > + break; > + } > + > + } > + > + finish_wait(&vblk->queue_wait, &wait); > +} > + > +static void virtblk_make_request(struct request_queue *q, struct bio *bio) > +{ > + struct virtio_blk *vblk = q->queuedata; > + unsigned int num, out = 0, in = 0; > + struct virtblk_req *vbr; > + > + BUG_ON(bio->bi_phys_segments + 2 > vblk->sg_elems); > + BUG_ON(bio->bi_rw & (REQ_FLUSH | REQ_FUA)); > + > + vbr = virtblk_alloc_req(vblk, GFP_NOIO); > + if (!vbr) { > + bio_endio(bio, -ENOMEM); > + return; > + } > + > + vbr->bio = bio; > + vbr->req = NULL; > + vbr->out_hdr.type = 0; > + vbr->out_hdr.sector = bio->bi_sector; > + vbr->out_hdr.ioprio = bio_prio(bio); > + > + sg_set_buf(&vbr->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr)); > + > + num = blk_bio_map_sg(q, bio, vbr->sg + out); > + > + sg_set_buf(&vbr->sg[num + out + in++], &vbr->status, > + sizeof(vbr->status)); > + > + if (num) { > + if (bio->bi_rw & REQ_WRITE) { > + vbr->out_hdr.type |= VIRTIO_BLK_T_OUT; > + out += num; > + } else { > + vbr->out_hdr.type |= VIRTIO_BLK_T_IN; > + in += num; > + } > + } > + > + spin_lock_irq(vblk->disk->queue->queue_lock); > + if (unlikely(virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr, > + GFP_ATOMIC) < 0)) { > + spin_unlock_irq(vblk->disk->queue->queue_lock); > + virtblk_add_buf_wait(vblk, vbr, out, in); > + return; > + } > + virtqueue_kick(vblk->vq); > + spin_unlock_irq(vblk->disk->queue->queue_lock); > +} > + > /* return id (s/n) string for *disk to *id_str > */ > static int virtblk_get_id(struct gendisk *disk, char *id_str) > @@ -360,7 +475,7 @@ static int init_vq(struct virtio_blk *vblk) > int err = 0; > > /* We expect one virtqueue, for output. */ > - vblk->vq = virtio_find_single_vq(vblk->vdev, blk_done, "requests"); > + vblk->vq = virtio_find_single_vq(vblk->vdev, virtblk_done, "requests"); > if (IS_ERR(vblk->vq)) > err = PTR_ERR(vblk->vq); > > @@ -414,7 +529,7 @@ static void virtblk_update_cache_mode(struct virtio_device *vdev) > u8 writeback = virtblk_get_cache_mode(vdev); > struct virtio_blk *vblk = vdev->priv; > > - if (writeback) > + if (writeback && !use_bio) > blk_queue_flush(vblk->disk->queue, REQ_FLUSH); > else > blk_queue_flush(vblk->disk->queue, 0); > @@ -477,6 +592,8 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) > struct virtio_blk *vblk; > struct request_queue *q; > int err, index; > + int pool_size; > + > u64 cap; > u32 v, blk_size, sg_elems, opt_io_size; > u16 min_io_size; > @@ -506,10 +623,12 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) > goto out_free_index; > } > > + init_waitqueue_head(&vblk->queue_wait); > vblk->vdev = vdev; > vblk->sg_elems = sg_elems; > sg_init_table(vblk->sg, vblk->sg_elems); > mutex_init(&vblk->config_lock); > + > INIT_WORK(&vblk->config_work, virtblk_config_changed_work); > vblk->config_enable = true; > > @@ -517,7 +636,10 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) > if (err) > goto out_free_vblk; > > - vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req)); > + pool_size = sizeof(struct virtblk_req); > + if (use_bio) > + pool_size += sizeof(struct scatterlist) * sg_elems; > + vblk->pool = mempool_create_kmalloc_pool(1, pool_size); > if (!vblk->pool) { > err = -ENOMEM; > goto out_free_vq; > @@ -530,12 +652,14 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) > goto out_mempool; > } > > - q = vblk->disk->queue = blk_init_queue(do_virtblk_request, NULL); > + q = vblk->disk->queue = blk_init_queue(virtblk_request, NULL); > if (!q) { > err = -ENOMEM; > goto out_put_disk; > } > > + if (use_bio) > + blk_queue_make_request(q, virtblk_make_request); > q->queuedata = vblk; > > virtblk_name_format("vd", index, vblk->disk->disk_name, DISK_NAME_LEN); > @@ -620,7 +744,6 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) > if (!err && opt_io_size) > blk_queue_io_opt(q, blk_size * opt_io_size); > > - > add_disk(vblk->disk); > err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_serial); > if (err) > -- > 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, 29 Jul 2012 14:11:15 +0300, "Michael S. Tsirkin" <mst@redhat.com> wrote: > On Sat, Jul 28, 2012 at 10:21:05AM +0800, Asias He wrote: > > This patch introduces bio-based IO path for virtio-blk. > > > > Compared to request-based IO path, bio-based IO path uses driver > > provided ->make_request_fn() method to bypasses the IO scheduler. It > > handles the bio to device directly without allocating a request in block > > layer. This reduces the IO path in guest kernel to achieve high IOPS > > and lower latency. The downside is that guest can not use the IO > > scheduler to merge and sort requests. However, this is not a big problem > > if the backend disk in host side uses faster disk device. > > If this optimization depends on the host, then it > should be reported to the guest using a feature bit, > as opposed to being guest driven. I consider this approach a half-way step. Quick attempts on my laptop and I couldn't find a case where the bio path was a loss, but in theory if the host wasn't doing any reordering and it was a slow device, you'd want the guest to do so. I'm not sure if current qemu can be configured to do such a thing? Cheers, Rusty. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 07/29/2012 07:11 PM, Michael S. Tsirkin wrote: > On Sat, Jul 28, 2012 at 10:21:05AM +0800, Asias He wrote: >> This patch introduces bio-based IO path for virtio-blk. >> >> Compared to request-based IO path, bio-based IO path uses driver >> provided ->make_request_fn() method to bypasses the IO scheduler. It >> handles the bio to device directly without allocating a request in block >> layer. This reduces the IO path in guest kernel to achieve high IOPS >> and lower latency. The downside is that guest can not use the IO >> scheduler to merge and sort requests. However, this is not a big problem >> if the backend disk in host side uses faster disk device. > > If this optimization depends on the host, then it > should be reported to the guest using a feature bit, > as opposed to being guest driven. > >> When the bio-based IO path is not enabled, virtio-blk still uses the >> original request-based IO path, no performance difference is observed. >> >> Performance evaluation: >> ----------------------------- >> 1) Fio test is performed in a 8 vcpu guest with ramdisk based guest using >> kvm tool. >> >> Short version: >> With bio-based IO path, sequential read/write, random read/write >> IOPS boost : 28%, 24%, 21%, 16% >> Latency improvement: 32%, 17%, 21%, 16% >> >> Long version: >> With bio-based IO path: >> seq-read : io=2048.0MB, bw=116996KB/s, iops=233991 , runt= 17925msec >> seq-write : io=2048.0MB, bw=100829KB/s, iops=201658 , runt= 20799msec >> rand-read : io=3095.7MB, bw=112134KB/s, iops=224268 , runt= 28269msec >> rand-write: io=3095.7MB, bw=96198KB/s, iops=192396 , runt= 32952msec >> clat (usec): min=0 , max=2631.6K, avg=58716.99, stdev=191377.30 >> clat (usec): min=0 , max=1753.2K, avg=66423.25, stdev=81774.35 >> clat (usec): min=0 , max=2915.5K, avg=61685.70, stdev=120598.39 >> clat (usec): min=0 , max=1933.4K, avg=76935.12, stdev=96603.45 >> cpu : usr=74.08%, sys=703.84%, ctx=29661403, majf=21354, minf=22460954 >> cpu : usr=70.92%, sys=702.81%, ctx=77219828, majf=13980, minf=27713137 >> cpu : usr=72.23%, sys=695.37%, ctx=88081059, majf=18475, minf=28177648 >> cpu : usr=69.69%, sys=654.13%, ctx=145476035, majf=15867, minf=26176375 >> With request-based IO path: >> seq-read : io=2048.0MB, bw=91074KB/s, iops=182147 , runt= 23027msec >> seq-write : io=2048.0MB, bw=80725KB/s, iops=161449 , runt= 25979msec >> rand-read : io=3095.7MB, bw=92106KB/s, iops=184211 , runt= 34416msec >> rand-write: io=3095.7MB, bw=82815KB/s, iops=165630 , runt= 38277msec >> clat (usec): min=0 , max=1932.4K, avg=77824.17, stdev=170339.49 >> clat (usec): min=0 , max=2510.2K, avg=78023.96, stdev=146949.15 >> clat (usec): min=0 , max=3037.2K, avg=74746.53, stdev=128498.27 >> clat (usec): min=0 , max=1363.4K, avg=89830.75, stdev=114279.68 >> cpu : usr=53.28%, sys=724.19%, ctx=37988895, majf=17531, minf=23577622 >> cpu : usr=49.03%, sys=633.20%, ctx=205935380, majf=18197, minf=27288959 >> cpu : usr=55.78%, sys=722.40%, ctx=101525058, majf=19273, minf=28067082 >> cpu : usr=56.55%, sys=690.83%, ctx=228205022, majf=18039, minf=26551985 > > > So bio based causes cpu to jump up by some 30%? > What happens if you divide IOPS/CPU? > Any improvement that comes from increasing the cpu share > of the given guest on the host will not scale well on > a typical overcommitted host. if you add sys and usr time up, the jump is that much. For ramdisk based device, bio-based ------------------ >>> 74.08 + 703.84 777.9200000000001 >>> 70.92 + 702.81 773.7299999999999 >>> 72.23 + 695.37 767.6 >>> 69.69 + 654.13 723.8199999999999 >>> 53.28 + 724.19 777.47 req-based ------------------ >>> 53.28 + 724.19 777.47 >>> 49.03 + 633.20 682.23 >>> 55.78 + 722.40 778.18 >>> 56.55 + 690.83 747.38 And for real device(fusion io), the cpu time is smaller with bio path. bio-based ------------------ >>> 56.79 + 421.70 478.49 >>> 61.81 + 455.53 517.3399999999999 >>> 63.10+455.38 518.48 >>> 62.04 + 453.58 515.62 req-based ------------------ >>> 44.08 + 590.71 634.7900000000001 >>> 48.73 + 610.78 659.51 >>> 45.58 + 581.16 626.74 >>> 48.40 + 599.65 648.05 > >> 2) Fio test is performed in a 8 vcpu guest with Fusion-IO based guest using >> kvm tool. >> >> Short version: >> With bio-based IO path, sequential read/write, random read/write >> IOPS boost : 11%, 11%, 13%, 10% >> Latency improvement: 10%, 10%, 12%, 10% >> Long Version: >> With bio-based IO path: >> read : io=2048.0MB, bw=58920KB/s, iops=117840 , runt= 35593msec >> write: io=2048.0MB, bw=64308KB/s, iops=128616 , runt= 32611msec >> read : io=3095.7MB, bw=59633KB/s, iops=119266 , runt= 53157msec >> write: io=3095.7MB, bw=62993KB/s, iops=125985 , runt= 50322msec >> clat (usec): min=0 , max=1284.3K, avg=128109.01, stdev=71513.29 >> clat (usec): min=94 , max=962339 , avg=116832.95, stdev=65836.80 >> clat (usec): min=0 , max=1846.6K, avg=128509.99, stdev=89575.07 >> clat (usec): min=0 , max=2256.4K, avg=121361.84, stdev=82747.25 >> cpu : usr=56.79%, sys=421.70%, ctx=147335118, majf=21080, minf=19852517 >> cpu : usr=61.81%, sys=455.53%, ctx=143269950, majf=16027, minf=24800604 >> cpu : usr=63.10%, sys=455.38%, ctx=178373538, majf=16958, minf=24822612 >> cpu : usr=62.04%, sys=453.58%, ctx=226902362, majf=16089, minf=23278105 >> With request-based IO path: >> read : io=2048.0MB, bw=52896KB/s, iops=105791 , runt= 39647msec >> write: io=2048.0MB, bw=57856KB/s, iops=115711 , runt= 36248msec >> read : io=3095.7MB, bw=52387KB/s, iops=104773 , runt= 60510msec >> write: io=3095.7MB, bw=57310KB/s, iops=114619 , runt= 55312msec >> clat (usec): min=0 , max=1532.6K, avg=142085.62, stdev=109196.84 >> clat (usec): min=0 , max=1487.4K, avg=129110.71, stdev=114973.64 >> clat (usec): min=0 , max=1388.6K, avg=145049.22, stdev=107232.55 >> clat (usec): min=0 , max=1465.9K, avg=133585.67, stdev=110322.95 >> cpu : usr=44.08%, sys=590.71%, ctx=451812322, majf=14841, minf=17648641 >> cpu : usr=48.73%, sys=610.78%, ctx=418953997, majf=22164, minf=26850689 >> cpu : usr=45.58%, sys=581.16%, ctx=714079216, majf=21497, minf=22558223 >> cpu : usr=48.40%, sys=599.65%, ctx=656089423, majf=16393, minf=23824409 > > > Is this host or guest cpu? We should probably measure host cpu > as this includes device overhead which could vary by load. It's guest cpu. Yes, host cpu is also interesting. > >> How to use: >> ----------------------------- >> Add 'virtio_blk.use_bio=1' to kernel cmdline or 'modprobe virtio_blk >> use_bio=1' to enable ->make_request_fn() based I/O path. >> >> Cc: Rusty Russell <rusty@rustcorp.com.au> >> Cc: "Michael S. Tsirkin" <mst@redhat.com> >> Cc: virtualization@lists.linux-foundation.org >> Cc: kvm@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org >> Acked-by: Rusty Russell <rusty@rustcorp.com.au> >> Signed-off-by: Christoph Hellwig <hch@lst.de> >> Signed-off-by: Minchan Kim <minchan.kim@gmail.com> >> Signed-off-by: Asias He <asias@redhat.com> >> --- >> drivers/block/virtio_blk.c | 203 +++++++++++++++++++++++++++++++++++--------- >> 1 file changed, 163 insertions(+), 40 deletions(-) >> >> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c >> index c0bbeb4..95cfeed 100644 >> --- a/drivers/block/virtio_blk.c >> +++ b/drivers/block/virtio_blk.c >> @@ -14,6 +14,9 @@ >> >> #define PART_BITS 4 >> >> +static bool use_bio; >> +module_param(use_bio, bool, S_IRUGO); >> + >> static int major; >> static DEFINE_IDA(vd_index_ida); >> >> @@ -23,6 +26,7 @@ struct virtio_blk >> { >> struct virtio_device *vdev; >> struct virtqueue *vq; >> + wait_queue_head_t queue_wait; >> >> /* The disk structure for the kernel. */ >> struct gendisk *disk; >> @@ -51,53 +55,87 @@ struct virtio_blk >> struct virtblk_req >> { >> struct request *req; >> + struct bio *bio; >> struct virtio_blk_outhdr out_hdr; >> struct virtio_scsi_inhdr in_hdr; >> u8 status; >> + struct scatterlist sg[]; >> }; >> >> -static void blk_done(struct virtqueue *vq) >> +static inline int virtblk_result(struct virtblk_req *vbr) >> +{ >> + switch (vbr->status) { >> + case VIRTIO_BLK_S_OK: >> + return 0; >> + case VIRTIO_BLK_S_UNSUPP: >> + return -ENOTTY; >> + default: >> + return -EIO; >> + } >> +} >> + >> +static inline void virtblk_request_done(struct virtio_blk *vblk, >> + struct virtblk_req *vbr) >> +{ >> + struct request *req = vbr->req; >> + int error = virtblk_result(vbr); >> + >> + if (req->cmd_type == REQ_TYPE_BLOCK_PC) { >> + req->resid_len = vbr->in_hdr.residual; >> + req->sense_len = vbr->in_hdr.sense_len; >> + req->errors = vbr->in_hdr.errors; >> + } else if (req->cmd_type == REQ_TYPE_SPECIAL) { >> + req->errors = (error != 0); >> + } >> + >> + __blk_end_request_all(req, error); >> + mempool_free(vbr, vblk->pool); >> +} >> + >> +static inline void virtblk_bio_done(struct virtio_blk *vblk, >> + struct virtblk_req *vbr) >> +{ >> + bio_endio(vbr->bio, virtblk_result(vbr)); >> + mempool_free(vbr, vblk->pool); >> +} >> + >> +static void virtblk_done(struct virtqueue *vq) >> { >> struct virtio_blk *vblk = vq->vdev->priv; >> + unsigned long bio_done = 0, req_done = 0; >> struct virtblk_req *vbr; >> - unsigned int len; >> unsigned long flags; >> + unsigned int len; >> >> spin_lock_irqsave(vblk->disk->queue->queue_lock, flags); >> while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) { >> - int error; >> - >> - switch (vbr->status) { >> - case VIRTIO_BLK_S_OK: >> - error = 0; >> - break; >> - case VIRTIO_BLK_S_UNSUPP: >> - error = -ENOTTY; >> - break; >> - default: >> - error = -EIO; >> - break; >> - } >> - >> - switch (vbr->req->cmd_type) { >> - case REQ_TYPE_BLOCK_PC: >> - vbr->req->resid_len = vbr->in_hdr.residual; >> - vbr->req->sense_len = vbr->in_hdr.sense_len; >> - vbr->req->errors = vbr->in_hdr.errors; >> - break; >> - case REQ_TYPE_SPECIAL: >> - vbr->req->errors = (error != 0); >> - break; >> - default: >> - break; >> + if (vbr->bio) { >> + virtblk_bio_done(vblk, vbr); >> + bio_done++; >> + } else { >> + virtblk_request_done(vblk, vbr); >> + req_done++; >> } >> - >> - __blk_end_request_all(vbr->req, error); >> - mempool_free(vbr, vblk->pool); >> } >> /* In case queue is stopped waiting for more buffers. */ >> - blk_start_queue(vblk->disk->queue); >> + if (req_done) >> + blk_start_queue(vblk->disk->queue); >> spin_unlock_irqrestore(vblk->disk->queue->queue_lock, flags); >> + >> + if (bio_done) >> + wake_up(&vblk->queue_wait); >> +} >> + >> +static inline struct virtblk_req *virtblk_alloc_req(struct virtio_blk *vblk, >> + gfp_t gfp_mask) >> +{ >> + struct virtblk_req *vbr; >> + >> + vbr = mempool_alloc(vblk->pool, gfp_mask); >> + if (vbr && use_bio) >> + sg_init_table(vbr->sg, vblk->sg_elems); >> + >> + return vbr; >> } >> >> static bool do_req(struct request_queue *q, struct virtio_blk *vblk, >> @@ -106,13 +144,13 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, >> unsigned long num, out = 0, in = 0; >> struct virtblk_req *vbr; >> >> - vbr = mempool_alloc(vblk->pool, GFP_ATOMIC); >> + vbr = virtblk_alloc_req(vblk, GFP_ATOMIC); >> if (!vbr) >> /* When another request finishes we'll try again. */ >> return false; >> >> vbr->req = req; >> - >> + vbr->bio = NULL; >> if (req->cmd_flags & REQ_FLUSH) { >> vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH; >> vbr->out_hdr.sector = 0; >> @@ -172,7 +210,8 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, >> } >> } >> >> - if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr, GFP_ATOMIC)<0) { >> + if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr, >> + GFP_ATOMIC) < 0) { >> mempool_free(vbr, vblk->pool); >> return false; >> } >> @@ -180,7 +219,7 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, >> return true; >> } >> >> -static void do_virtblk_request(struct request_queue *q) >> +static void virtblk_request(struct request_queue *q) >> { >> struct virtio_blk *vblk = q->queuedata; >> struct request *req; >> @@ -203,6 +242,82 @@ static void do_virtblk_request(struct request_queue *q) >> virtqueue_kick(vblk->vq); >> } >> >> +static void virtblk_add_buf_wait(struct virtio_blk *vblk, >> + struct virtblk_req *vbr, >> + unsigned long out, >> + unsigned long in) >> +{ >> + DEFINE_WAIT(wait); >> + >> + for (;;) { >> + prepare_to_wait_exclusive(&vblk->queue_wait, &wait, >> + TASK_UNINTERRUPTIBLE); >> + >> + spin_lock_irq(vblk->disk->queue->queue_lock); >> + if (virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr, >> + GFP_ATOMIC) < 0) { >> + spin_unlock_irq(vblk->disk->queue->queue_lock); >> + io_schedule(); >> + } else { >> + virtqueue_kick(vblk->vq); >> + spin_unlock_irq(vblk->disk->queue->queue_lock); >> + break; >> + } >> + >> + } >> + >> + finish_wait(&vblk->queue_wait, &wait); >> +} >> + >> +static void virtblk_make_request(struct request_queue *q, struct bio *bio) >> +{ >> + struct virtio_blk *vblk = q->queuedata; >> + unsigned int num, out = 0, in = 0; >> + struct virtblk_req *vbr; >> + >> + BUG_ON(bio->bi_phys_segments + 2 > vblk->sg_elems); >> + BUG_ON(bio->bi_rw & (REQ_FLUSH | REQ_FUA)); >> + >> + vbr = virtblk_alloc_req(vblk, GFP_NOIO); >> + if (!vbr) { >> + bio_endio(bio, -ENOMEM); >> + return; >> + } >> + >> + vbr->bio = bio; >> + vbr->req = NULL; >> + vbr->out_hdr.type = 0; >> + vbr->out_hdr.sector = bio->bi_sector; >> + vbr->out_hdr.ioprio = bio_prio(bio); >> + >> + sg_set_buf(&vbr->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr)); >> + >> + num = blk_bio_map_sg(q, bio, vbr->sg + out); >> + >> + sg_set_buf(&vbr->sg[num + out + in++], &vbr->status, >> + sizeof(vbr->status)); >> + >> + if (num) { >> + if (bio->bi_rw & REQ_WRITE) { >> + vbr->out_hdr.type |= VIRTIO_BLK_T_OUT; >> + out += num; >> + } else { >> + vbr->out_hdr.type |= VIRTIO_BLK_T_IN; >> + in += num; >> + } >> + } >> + >> + spin_lock_irq(vblk->disk->queue->queue_lock); >> + if (unlikely(virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr, >> + GFP_ATOMIC) < 0)) { >> + spin_unlock_irq(vblk->disk->queue->queue_lock); >> + virtblk_add_buf_wait(vblk, vbr, out, in); >> + return; >> + } >> + virtqueue_kick(vblk->vq); >> + spin_unlock_irq(vblk->disk->queue->queue_lock); >> +} >> + >> /* return id (s/n) string for *disk to *id_str >> */ >> static int virtblk_get_id(struct gendisk *disk, char *id_str) >> @@ -360,7 +475,7 @@ static int init_vq(struct virtio_blk *vblk) >> int err = 0; >> >> /* We expect one virtqueue, for output. */ >> - vblk->vq = virtio_find_single_vq(vblk->vdev, blk_done, "requests"); >> + vblk->vq = virtio_find_single_vq(vblk->vdev, virtblk_done, "requests"); >> if (IS_ERR(vblk->vq)) >> err = PTR_ERR(vblk->vq); >> >> @@ -414,7 +529,7 @@ static void virtblk_update_cache_mode(struct virtio_device *vdev) >> u8 writeback = virtblk_get_cache_mode(vdev); >> struct virtio_blk *vblk = vdev->priv; >> >> - if (writeback) >> + if (writeback && !use_bio) >> blk_queue_flush(vblk->disk->queue, REQ_FLUSH); >> else >> blk_queue_flush(vblk->disk->queue, 0); >> @@ -477,6 +592,8 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) >> struct virtio_blk *vblk; >> struct request_queue *q; >> int err, index; >> + int pool_size; >> + >> u64 cap; >> u32 v, blk_size, sg_elems, opt_io_size; >> u16 min_io_size; >> @@ -506,10 +623,12 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) >> goto out_free_index; >> } >> >> + init_waitqueue_head(&vblk->queue_wait); >> vblk->vdev = vdev; >> vblk->sg_elems = sg_elems; >> sg_init_table(vblk->sg, vblk->sg_elems); >> mutex_init(&vblk->config_lock); >> + >> INIT_WORK(&vblk->config_work, virtblk_config_changed_work); >> vblk->config_enable = true; >> >> @@ -517,7 +636,10 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) >> if (err) >> goto out_free_vblk; >> >> - vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req)); >> + pool_size = sizeof(struct virtblk_req); >> + if (use_bio) >> + pool_size += sizeof(struct scatterlist) * sg_elems; >> + vblk->pool = mempool_create_kmalloc_pool(1, pool_size); >> if (!vblk->pool) { >> err = -ENOMEM; >> goto out_free_vq; >> @@ -530,12 +652,14 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) >> goto out_mempool; >> } >> >> - q = vblk->disk->queue = blk_init_queue(do_virtblk_request, NULL); >> + q = vblk->disk->queue = blk_init_queue(virtblk_request, NULL); >> if (!q) { >> err = -ENOMEM; >> goto out_put_disk; >> } >> >> + if (use_bio) >> + blk_queue_make_request(q, virtblk_make_request); >> q->queuedata = vblk; >> >> virtblk_name_format("vd", index, vblk->disk->disk_name, DISK_NAME_LEN); >> @@ -620,7 +744,6 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) >> if (!err && opt_io_size) >> blk_queue_io_opt(q, blk_size * opt_io_size); >> >> - >> add_disk(vblk->disk); >> err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_serial); >> if (err) >> -- >> 1.7.10.4
Hello Sasha, On 07/28/2012 02:35 PM, Sasha Levin wrote: > On 07/28/2012 04:21 AM, Asias He wrote: >> This patch introduces bio-based IO path for virtio-blk. >> >> Compared to request-based IO path, bio-based IO path uses driver >> provided ->make_request_fn() method to bypasses the IO scheduler. It >> handles the bio to device directly without allocating a request in block >> layer. This reduces the IO path in guest kernel to achieve high IOPS >> and lower latency. The downside is that guest can not use the IO >> scheduler to merge and sort requests. However, this is not a big problem >> if the backend disk in host side uses faster disk device. >> >> When the bio-based IO path is not enabled, virtio-blk still uses the >> original request-based IO path, no performance difference is observed. >> >> Performance evaluation: >> ----------------------------- >> 1) Fio test is performed in a 8 vcpu guest with ramdisk based guest using >> kvm tool. >> >> Short version: >> With bio-based IO path, sequential read/write, random read/write >> IOPS boost : 28%, 24%, 21%, 16% >> Latency improvement: 32%, 17%, 21%, 16% >> >> Long version: >> With bio-based IO path: >> seq-read : io=2048.0MB, bw=116996KB/s, iops=233991 , runt= 17925msec >> seq-write : io=2048.0MB, bw=100829KB/s, iops=201658 , runt= 20799msec >> rand-read : io=3095.7MB, bw=112134KB/s, iops=224268 , runt= 28269msec >> rand-write: io=3095.7MB, bw=96198KB/s, iops=192396 , runt= 32952msec >> clat (usec): min=0 , max=2631.6K, avg=58716.99, stdev=191377.30 >> clat (usec): min=0 , max=1753.2K, avg=66423.25, stdev=81774.35 >> clat (usec): min=0 , max=2915.5K, avg=61685.70, stdev=120598.39 >> clat (usec): min=0 , max=1933.4K, avg=76935.12, stdev=96603.45 >> cpu : usr=74.08%, sys=703.84%, ctx=29661403, majf=21354, minf=22460954 >> cpu : usr=70.92%, sys=702.81%, ctx=77219828, majf=13980, minf=27713137 >> cpu : usr=72.23%, sys=695.37%, ctx=88081059, majf=18475, minf=28177648 >> cpu : usr=69.69%, sys=654.13%, ctx=145476035, majf=15867, minf=26176375 >> With request-based IO path: >> seq-read : io=2048.0MB, bw=91074KB/s, iops=182147 , runt= 23027msec >> seq-write : io=2048.0MB, bw=80725KB/s, iops=161449 , runt= 25979msec >> rand-read : io=3095.7MB, bw=92106KB/s, iops=184211 , runt= 34416msec >> rand-write: io=3095.7MB, bw=82815KB/s, iops=165630 , runt= 38277msec >> clat (usec): min=0 , max=1932.4K, avg=77824.17, stdev=170339.49 >> clat (usec): min=0 , max=2510.2K, avg=78023.96, stdev=146949.15 >> clat (usec): min=0 , max=3037.2K, avg=74746.53, stdev=128498.27 >> clat (usec): min=0 , max=1363.4K, avg=89830.75, stdev=114279.68 >> cpu : usr=53.28%, sys=724.19%, ctx=37988895, majf=17531, minf=23577622 >> cpu : usr=49.03%, sys=633.20%, ctx=205935380, majf=18197, minf=27288959 >> cpu : usr=55.78%, sys=722.40%, ctx=101525058, majf=19273, minf=28067082 >> cpu : usr=56.55%, sys=690.83%, ctx=228205022, majf=18039, minf=26551985 >> >> 2) Fio test is performed in a 8 vcpu guest with Fusion-IO based guest using >> kvm tool. >> >> Short version: >> With bio-based IO path, sequential read/write, random read/write >> IOPS boost : 11%, 11%, 13%, 10% >> Latency improvement: 10%, 10%, 12%, 10% >> Long Version: >> With bio-based IO path: >> read : io=2048.0MB, bw=58920KB/s, iops=117840 , runt= 35593msec >> write: io=2048.0MB, bw=64308KB/s, iops=128616 , runt= 32611msec >> read : io=3095.7MB, bw=59633KB/s, iops=119266 , runt= 53157msec >> write: io=3095.7MB, bw=62993KB/s, iops=125985 , runt= 50322msec >> clat (usec): min=0 , max=1284.3K, avg=128109.01, stdev=71513.29 >> clat (usec): min=94 , max=962339 , avg=116832.95, stdev=65836.80 >> clat (usec): min=0 , max=1846.6K, avg=128509.99, stdev=89575.07 >> clat (usec): min=0 , max=2256.4K, avg=121361.84, stdev=82747.25 >> cpu : usr=56.79%, sys=421.70%, ctx=147335118, majf=21080, minf=19852517 >> cpu : usr=61.81%, sys=455.53%, ctx=143269950, majf=16027, minf=24800604 >> cpu : usr=63.10%, sys=455.38%, ctx=178373538, majf=16958, minf=24822612 >> cpu : usr=62.04%, sys=453.58%, ctx=226902362, majf=16089, minf=23278105 >> With request-based IO path: >> read : io=2048.0MB, bw=52896KB/s, iops=105791 , runt= 39647msec >> write: io=2048.0MB, bw=57856KB/s, iops=115711 , runt= 36248msec >> read : io=3095.7MB, bw=52387KB/s, iops=104773 , runt= 60510msec >> write: io=3095.7MB, bw=57310KB/s, iops=114619 , runt= 55312msec >> clat (usec): min=0 , max=1532.6K, avg=142085.62, stdev=109196.84 >> clat (usec): min=0 , max=1487.4K, avg=129110.71, stdev=114973.64 >> clat (usec): min=0 , max=1388.6K, avg=145049.22, stdev=107232.55 >> clat (usec): min=0 , max=1465.9K, avg=133585.67, stdev=110322.95 >> cpu : usr=44.08%, sys=590.71%, ctx=451812322, majf=14841, minf=17648641 >> cpu : usr=48.73%, sys=610.78%, ctx=418953997, majf=22164, minf=26850689 >> cpu : usr=45.58%, sys=581.16%, ctx=714079216, majf=21497, minf=22558223 >> cpu : usr=48.40%, sys=599.65%, ctx=656089423, majf=16393, minf=23824409 > > What are the cases where we'll see a performance degradation with using the bio path? Could we measure performance for those as well? > >> How to use: >> ----------------------------- >> Add 'virtio_blk.use_bio=1' to kernel cmdline or 'modprobe virtio_blk >> use_bio=1' to enable ->make_request_fn() based I/O path. > > If there are, in fact, no cases where performance is degraded, can use_bio=1 be the default? Here are some results on a SATA based image file. In this case, the bio path is slower than req path doing sequential read/write. qemu use_bio=0 (req-based) ------------------------------------- read : io=120964KB, bw=26098KB/s, iops=6470 , runt= 4635msec write: io=190236KB, bw=35505KB/s, iops=8829 , runt= 5358msec read : io=257400KB, bw=1963.7KB/s, iops=488 , runt=131081msec write: io=258944KB, bw=1302.7KB/s, iops=324 , runt=198872msec clat (msec): min=1 , max=1527 , avg=30.73, stdev=144.73 clat (usec): min=811 , max=247072 , avg=28451.71, stdev=16107.22 clat (msec): min=6 , max=2519 , avg=513.91, stdev=231.07 clat (msec): min=33 , max=2621 , avg=772.33, stdev=348.39 cpu : usr=4.05%, sys=14.56%, ctx=38199, majf=0, minf=4 cpu : usr=4.02%, sys=15.48%, ctx=53724, majf=0, minf=0 cpu : usr=0.15%, sys=0.30%, ctx=20535, majf=0, minf=16 cpu : usr=0.32%, sys=0.96%, ctx=101465, majf=0, minf=0 qemu use_bio=1 (bio-based) ------------------------------------- read : io=202736KB, bw=25569KB/s, iops=6360 , runt= 7929msec write: io=217844KB, bw=20335KB/s, iops=5060 , runt= 10713msec read : io=256980KB, bw=1958.2KB/s, iops=487 , runt=131235msec write: io=258288KB, bw=1423.9KB/s, iops=354 , runt=181405msec clat (usec): min=922 , max=1578.2K, avg=38702.18, stdev=99248.33 clat (usec): min=460 , max=241314 , avg=49326.52, stdev=18705.68 clat (msec): min=19 , max=2370 , avg=515.30, stdev=200.84 clat (msec): min=11 , max=3751 , avg=702.60, stdev=286.93 cpu : usr=2.54%, sys=8.75%, ctx=68522, majf=0, minf=6 cpu : usr=1.96%, sys=7.70%, ctx=70003, majf=0, minf=0 cpu : usr=0.39%, sys=1.46%, ctx=259459, majf=0, minf=16 cpu : usr=0.28%, sys=1.21%, ctx=265148, majf=0, minf=0 lkvm use_bio=0 (req-based) ------------------------------------- read : io=150120KB, bw=40420KB/s, iops=10037 , runt= 3714msec write: io=194932KB, bw=27029KB/s, iops=6722 , runt= 7212msec read : io=257136KB, bw=2001.1KB/s, iops=498 , runt=128443msec write: io=258276KB, bw=1537.2KB/s, iops=382 , runt=168028msec clat (msec): min=1 , max=1542 , avg=24.84, stdev=32.45 clat (msec): min=3 , max=628 , avg=35.62, stdev=39.71 clat (msec): min=8 , max=2540 , avg=503.28, stdev=236.97 clat (msec): min=41 , max=4398 , avg=653.88, stdev=302.61 cpu : usr=3.91%, sys=15.75%, ctx=26968, majf=0, minf=23 cpu : usr=2.50%, sys=10.56%, ctx=19090, majf=0, minf=0 cpu : usr=0.16%, sys=0.43%, ctx=20159, majf=0, minf=16 cpu : usr=0.18%, sys=0.53%, ctx=81364, majf=0, minf=0 lkvm use_bio=1 (bio-based) ------------------------------------- read : io=124812KB, bw=36537KB/s, iops=9060 , runt= 3416msec write: io=169180KB, bw=24406KB/s, iops=6065 , runt= 6932msec read : io=256200KB, bw=2089.3KB/s, iops=520 , runt=122630msec write: io=257988KB, bw=1545.7KB/s, iops=384 , runt=166910msec clat (msec): min=1 , max=1527 , avg=28.06, stdev=89.54 clat (msec): min=2 , max=344 , avg=41.12, stdev=38.70 clat (msec): min=8 , max=1984 , avg=490.63, stdev=207.28 clat (msec): min=33 , max=4131 , avg=659.19, stdev=304.71 cpu : usr=4.85%, sys=17.15%, ctx=31593, majf=0, minf=7 cpu : usr=3.04%, sys=11.45%, ctx=39377, majf=0, minf=0 cpu : usr=0.47%, sys=1.59%, ctx=262986, majf=0, minf=16 cpu : usr=0.47%, sys=1.46%, ctx=337410, majf=0, minf=0
On Mon, Jul 30, 2012 at 11:25:51AM +0930, Rusty Russell wrote: > I consider this approach a half-way step. Quick attempts on my laptop > and I couldn't find a case where the bio path was a loss, but in theory > if the host wasn't doing any reordering and it was a slow device, you'd > want the guest to do so. > > I'm not sure if current qemu can be configured to do such a thing? The host kernel will do the I/O scheduling for you unless you explicitly disable it. And we should be able to assume an administrator will only disable it when they have a reason for it - if not they'll get worse performance for non-virtualized workloads as well. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index c0bbeb4..95cfeed 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -14,6 +14,9 @@ #define PART_BITS 4 +static bool use_bio; +module_param(use_bio, bool, S_IRUGO); + static int major; static DEFINE_IDA(vd_index_ida); @@ -23,6 +26,7 @@ struct virtio_blk { struct virtio_device *vdev; struct virtqueue *vq; + wait_queue_head_t queue_wait; /* The disk structure for the kernel. */ struct gendisk *disk; @@ -51,53 +55,87 @@ struct virtio_blk struct virtblk_req { struct request *req; + struct bio *bio; struct virtio_blk_outhdr out_hdr; struct virtio_scsi_inhdr in_hdr; u8 status; + struct scatterlist sg[]; }; -static void blk_done(struct virtqueue *vq) +static inline int virtblk_result(struct virtblk_req *vbr) +{ + switch (vbr->status) { + case VIRTIO_BLK_S_OK: + return 0; + case VIRTIO_BLK_S_UNSUPP: + return -ENOTTY; + default: + return -EIO; + } +} + +static inline void virtblk_request_done(struct virtio_blk *vblk, + struct virtblk_req *vbr) +{ + struct request *req = vbr->req; + int error = virtblk_result(vbr); + + if (req->cmd_type == REQ_TYPE_BLOCK_PC) { + req->resid_len = vbr->in_hdr.residual; + req->sense_len = vbr->in_hdr.sense_len; + req->errors = vbr->in_hdr.errors; + } else if (req->cmd_type == REQ_TYPE_SPECIAL) { + req->errors = (error != 0); + } + + __blk_end_request_all(req, error); + mempool_free(vbr, vblk->pool); +} + +static inline void virtblk_bio_done(struct virtio_blk *vblk, + struct virtblk_req *vbr) +{ + bio_endio(vbr->bio, virtblk_result(vbr)); + mempool_free(vbr, vblk->pool); +} + +static void virtblk_done(struct virtqueue *vq) { struct virtio_blk *vblk = vq->vdev->priv; + unsigned long bio_done = 0, req_done = 0; struct virtblk_req *vbr; - unsigned int len; unsigned long flags; + unsigned int len; spin_lock_irqsave(vblk->disk->queue->queue_lock, flags); while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) { - int error; - - switch (vbr->status) { - case VIRTIO_BLK_S_OK: - error = 0; - break; - case VIRTIO_BLK_S_UNSUPP: - error = -ENOTTY; - break; - default: - error = -EIO; - break; - } - - switch (vbr->req->cmd_type) { - case REQ_TYPE_BLOCK_PC: - vbr->req->resid_len = vbr->in_hdr.residual; - vbr->req->sense_len = vbr->in_hdr.sense_len; - vbr->req->errors = vbr->in_hdr.errors; - break; - case REQ_TYPE_SPECIAL: - vbr->req->errors = (error != 0); - break; - default: - break; + if (vbr->bio) { + virtblk_bio_done(vblk, vbr); + bio_done++; + } else { + virtblk_request_done(vblk, vbr); + req_done++; } - - __blk_end_request_all(vbr->req, error); - mempool_free(vbr, vblk->pool); } /* In case queue is stopped waiting for more buffers. */ - blk_start_queue(vblk->disk->queue); + if (req_done) + blk_start_queue(vblk->disk->queue); spin_unlock_irqrestore(vblk->disk->queue->queue_lock, flags); + + if (bio_done) + wake_up(&vblk->queue_wait); +} + +static inline struct virtblk_req *virtblk_alloc_req(struct virtio_blk *vblk, + gfp_t gfp_mask) +{ + struct virtblk_req *vbr; + + vbr = mempool_alloc(vblk->pool, gfp_mask); + if (vbr && use_bio) + sg_init_table(vbr->sg, vblk->sg_elems); + + return vbr; } static bool do_req(struct request_queue *q, struct virtio_blk *vblk, @@ -106,13 +144,13 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, unsigned long num, out = 0, in = 0; struct virtblk_req *vbr; - vbr = mempool_alloc(vblk->pool, GFP_ATOMIC); + vbr = virtblk_alloc_req(vblk, GFP_ATOMIC); if (!vbr) /* When another request finishes we'll try again. */ return false; vbr->req = req; - + vbr->bio = NULL; if (req->cmd_flags & REQ_FLUSH) { vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH; vbr->out_hdr.sector = 0; @@ -172,7 +210,8 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, } } - if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr, GFP_ATOMIC)<0) { + if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr, + GFP_ATOMIC) < 0) { mempool_free(vbr, vblk->pool); return false; } @@ -180,7 +219,7 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, return true; } -static void do_virtblk_request(struct request_queue *q) +static void virtblk_request(struct request_queue *q) { struct virtio_blk *vblk = q->queuedata; struct request *req; @@ -203,6 +242,82 @@ static void do_virtblk_request(struct request_queue *q) virtqueue_kick(vblk->vq); } +static void virtblk_add_buf_wait(struct virtio_blk *vblk, + struct virtblk_req *vbr, + unsigned long out, + unsigned long in) +{ + DEFINE_WAIT(wait); + + for (;;) { + prepare_to_wait_exclusive(&vblk->queue_wait, &wait, + TASK_UNINTERRUPTIBLE); + + spin_lock_irq(vblk->disk->queue->queue_lock); + if (virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr, + GFP_ATOMIC) < 0) { + spin_unlock_irq(vblk->disk->queue->queue_lock); + io_schedule(); + } else { + virtqueue_kick(vblk->vq); + spin_unlock_irq(vblk->disk->queue->queue_lock); + break; + } + + } + + finish_wait(&vblk->queue_wait, &wait); +} + +static void virtblk_make_request(struct request_queue *q, struct bio *bio) +{ + struct virtio_blk *vblk = q->queuedata; + unsigned int num, out = 0, in = 0; + struct virtblk_req *vbr; + + BUG_ON(bio->bi_phys_segments + 2 > vblk->sg_elems); + BUG_ON(bio->bi_rw & (REQ_FLUSH | REQ_FUA)); + + vbr = virtblk_alloc_req(vblk, GFP_NOIO); + if (!vbr) { + bio_endio(bio, -ENOMEM); + return; + } + + vbr->bio = bio; + vbr->req = NULL; + vbr->out_hdr.type = 0; + vbr->out_hdr.sector = bio->bi_sector; + vbr->out_hdr.ioprio = bio_prio(bio); + + sg_set_buf(&vbr->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr)); + + num = blk_bio_map_sg(q, bio, vbr->sg + out); + + sg_set_buf(&vbr->sg[num + out + in++], &vbr->status, + sizeof(vbr->status)); + + if (num) { + if (bio->bi_rw & REQ_WRITE) { + vbr->out_hdr.type |= VIRTIO_BLK_T_OUT; + out += num; + } else { + vbr->out_hdr.type |= VIRTIO_BLK_T_IN; + in += num; + } + } + + spin_lock_irq(vblk->disk->queue->queue_lock); + if (unlikely(virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr, + GFP_ATOMIC) < 0)) { + spin_unlock_irq(vblk->disk->queue->queue_lock); + virtblk_add_buf_wait(vblk, vbr, out, in); + return; + } + virtqueue_kick(vblk->vq); + spin_unlock_irq(vblk->disk->queue->queue_lock); +} + /* return id (s/n) string for *disk to *id_str */ static int virtblk_get_id(struct gendisk *disk, char *id_str) @@ -360,7 +475,7 @@ static int init_vq(struct virtio_blk *vblk) int err = 0; /* We expect one virtqueue, for output. */ - vblk->vq = virtio_find_single_vq(vblk->vdev, blk_done, "requests"); + vblk->vq = virtio_find_single_vq(vblk->vdev, virtblk_done, "requests"); if (IS_ERR(vblk->vq)) err = PTR_ERR(vblk->vq); @@ -414,7 +529,7 @@ static void virtblk_update_cache_mode(struct virtio_device *vdev) u8 writeback = virtblk_get_cache_mode(vdev); struct virtio_blk *vblk = vdev->priv; - if (writeback) + if (writeback && !use_bio) blk_queue_flush(vblk->disk->queue, REQ_FLUSH); else blk_queue_flush(vblk->disk->queue, 0); @@ -477,6 +592,8 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) struct virtio_blk *vblk; struct request_queue *q; int err, index; + int pool_size; + u64 cap; u32 v, blk_size, sg_elems, opt_io_size; u16 min_io_size; @@ -506,10 +623,12 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) goto out_free_index; } + init_waitqueue_head(&vblk->queue_wait); vblk->vdev = vdev; vblk->sg_elems = sg_elems; sg_init_table(vblk->sg, vblk->sg_elems); mutex_init(&vblk->config_lock); + INIT_WORK(&vblk->config_work, virtblk_config_changed_work); vblk->config_enable = true; @@ -517,7 +636,10 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) if (err) goto out_free_vblk; - vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req)); + pool_size = sizeof(struct virtblk_req); + if (use_bio) + pool_size += sizeof(struct scatterlist) * sg_elems; + vblk->pool = mempool_create_kmalloc_pool(1, pool_size); if (!vblk->pool) { err = -ENOMEM; goto out_free_vq; @@ -530,12 +652,14 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) goto out_mempool; } - q = vblk->disk->queue = blk_init_queue(do_virtblk_request, NULL); + q = vblk->disk->queue = blk_init_queue(virtblk_request, NULL); if (!q) { err = -ENOMEM; goto out_put_disk; } + if (use_bio) + blk_queue_make_request(q, virtblk_make_request); q->queuedata = vblk; virtblk_name_format("vd", index, vblk->disk->disk_name, DISK_NAME_LEN); @@ -620,7 +744,6 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) if (!err && opt_io_size) blk_queue_io_opt(q, blk_size * opt_io_size); - add_disk(vblk->disk); err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_serial); if (err)
This patch introduces bio-based IO path for virtio-blk. Compared to request-based IO path, bio-based IO path uses driver provided ->make_request_fn() method to bypasses the IO scheduler. It handles the bio to device directly without allocating a request in block layer. This reduces the IO path in guest kernel to achieve high IOPS and lower latency. The downside is that guest can not use the IO scheduler to merge and sort requests. However, this is not a big problem if the backend disk in host side uses faster disk device. When the bio-based IO path is not enabled, virtio-blk still uses the original request-based IO path, no performance difference is observed. Performance evaluation: ----------------------------- 1) Fio test is performed in a 8 vcpu guest with ramdisk based guest using kvm tool. Short version: With bio-based IO path, sequential read/write, random read/write IOPS boost : 28%, 24%, 21%, 16% Latency improvement: 32%, 17%, 21%, 16% Long version: With bio-based IO path: seq-read : io=2048.0MB, bw=116996KB/s, iops=233991 , runt= 17925msec seq-write : io=2048.0MB, bw=100829KB/s, iops=201658 , runt= 20799msec rand-read : io=3095.7MB, bw=112134KB/s, iops=224268 , runt= 28269msec rand-write: io=3095.7MB, bw=96198KB/s, iops=192396 , runt= 32952msec clat (usec): min=0 , max=2631.6K, avg=58716.99, stdev=191377.30 clat (usec): min=0 , max=1753.2K, avg=66423.25, stdev=81774.35 clat (usec): min=0 , max=2915.5K, avg=61685.70, stdev=120598.39 clat (usec): min=0 , max=1933.4K, avg=76935.12, stdev=96603.45 cpu : usr=74.08%, sys=703.84%, ctx=29661403, majf=21354, minf=22460954 cpu : usr=70.92%, sys=702.81%, ctx=77219828, majf=13980, minf=27713137 cpu : usr=72.23%, sys=695.37%, ctx=88081059, majf=18475, minf=28177648 cpu : usr=69.69%, sys=654.13%, ctx=145476035, majf=15867, minf=26176375 With request-based IO path: seq-read : io=2048.0MB, bw=91074KB/s, iops=182147 , runt= 23027msec seq-write : io=2048.0MB, bw=80725KB/s, iops=161449 , runt= 25979msec rand-read : io=3095.7MB, bw=92106KB/s, iops=184211 , runt= 34416msec rand-write: io=3095.7MB, bw=82815KB/s, iops=165630 , runt= 38277msec clat (usec): min=0 , max=1932.4K, avg=77824.17, stdev=170339.49 clat (usec): min=0 , max=2510.2K, avg=78023.96, stdev=146949.15 clat (usec): min=0 , max=3037.2K, avg=74746.53, stdev=128498.27 clat (usec): min=0 , max=1363.4K, avg=89830.75, stdev=114279.68 cpu : usr=53.28%, sys=724.19%, ctx=37988895, majf=17531, minf=23577622 cpu : usr=49.03%, sys=633.20%, ctx=205935380, majf=18197, minf=27288959 cpu : usr=55.78%, sys=722.40%, ctx=101525058, majf=19273, minf=28067082 cpu : usr=56.55%, sys=690.83%, ctx=228205022, majf=18039, minf=26551985 2) Fio test is performed in a 8 vcpu guest with Fusion-IO based guest using kvm tool. Short version: With bio-based IO path, sequential read/write, random read/write IOPS boost : 11%, 11%, 13%, 10% Latency improvement: 10%, 10%, 12%, 10% Long Version: With bio-based IO path: read : io=2048.0MB, bw=58920KB/s, iops=117840 , runt= 35593msec write: io=2048.0MB, bw=64308KB/s, iops=128616 , runt= 32611msec read : io=3095.7MB, bw=59633KB/s, iops=119266 , runt= 53157msec write: io=3095.7MB, bw=62993KB/s, iops=125985 , runt= 50322msec clat (usec): min=0 , max=1284.3K, avg=128109.01, stdev=71513.29 clat (usec): min=94 , max=962339 , avg=116832.95, stdev=65836.80 clat (usec): min=0 , max=1846.6K, avg=128509.99, stdev=89575.07 clat (usec): min=0 , max=2256.4K, avg=121361.84, stdev=82747.25 cpu : usr=56.79%, sys=421.70%, ctx=147335118, majf=21080, minf=19852517 cpu : usr=61.81%, sys=455.53%, ctx=143269950, majf=16027, minf=24800604 cpu : usr=63.10%, sys=455.38%, ctx=178373538, majf=16958, minf=24822612 cpu : usr=62.04%, sys=453.58%, ctx=226902362, majf=16089, minf=23278105 With request-based IO path: read : io=2048.0MB, bw=52896KB/s, iops=105791 , runt= 39647msec write: io=2048.0MB, bw=57856KB/s, iops=115711 , runt= 36248msec read : io=3095.7MB, bw=52387KB/s, iops=104773 , runt= 60510msec write: io=3095.7MB, bw=57310KB/s, iops=114619 , runt= 55312msec clat (usec): min=0 , max=1532.6K, avg=142085.62, stdev=109196.84 clat (usec): min=0 , max=1487.4K, avg=129110.71, stdev=114973.64 clat (usec): min=0 , max=1388.6K, avg=145049.22, stdev=107232.55 clat (usec): min=0 , max=1465.9K, avg=133585.67, stdev=110322.95 cpu : usr=44.08%, sys=590.71%, ctx=451812322, majf=14841, minf=17648641 cpu : usr=48.73%, sys=610.78%, ctx=418953997, majf=22164, minf=26850689 cpu : usr=45.58%, sys=581.16%, ctx=714079216, majf=21497, minf=22558223 cpu : usr=48.40%, sys=599.65%, ctx=656089423, majf=16393, minf=23824409 How to use: ----------------------------- Add 'virtio_blk.use_bio=1' to kernel cmdline or 'modprobe virtio_blk use_bio=1' to enable ->make_request_fn() based I/O path. Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: virtualization@lists.linux-foundation.org Cc: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org Acked-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Minchan Kim <minchan.kim@gmail.com> Signed-off-by: Asias He <asias@redhat.com> --- drivers/block/virtio_blk.c | 203 +++++++++++++++++++++++++++++++++++--------- 1 file changed, 163 insertions(+), 40 deletions(-)