| Message ID | 20210608131634.423904-4-pbonzini@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: file-posix queue | expand |
On Tue, Jun 08, 2021 at 03:16:30PM +0200, Paolo Bonzini wrote: > For block host devices, I/O can happen through either the kernel file > descriptor I/O system calls (preadv/pwritev, io_submit, io_uring) > or the SCSI passthrough ioctl SG_IO. > > In the latter case, the size of each transfer can be limited by the > HBA, while for file descriptor I/O the kernel is able to split and > merge I/O in smaller pieces as needed. Applying the HBA limits to > file descriptor I/O results in more system calls and suboptimal > performance, so this patch splits the max_transfer limit in two: > max_transfer remains valid and is used in general, while max_hw_transfer > is limited to the maximum hardware size. max_hw_transfer can then be > included by the scsi-generic driver in the block limits page, to ensure > that the stricter hardware limit is used. > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > block/block-backend.c | 12 ++++++++++++ > block/file-posix.c | 2 +- > block/io.c | 1 + > hw/scsi/scsi-generic.c | 2 +- > include/block/block_int.h | 7 +++++++ > include/sysemu/block-backend.h | 1 + [you can use git's orderfile option to put .h changes first] > 6 files changed, 23 insertions(+), 2 deletions(-) > > diff --git a/block/block-backend.c b/block/block-backend.c > index 15f1ea4288..2ea1412a54 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c > @@ -1953,6 +1953,18 @@ uint32_t blk_get_request_alignment(BlockBackend *blk) > return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE; > } > > +/* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero */ > +uint64_t blk_get_max_hw_transfer(BlockBackend *blk) Since we have declared (elsewhere) that the maximum block device is signed, would this be better as int64_t? (Our reasoning is that off_t is also signed, and we are unlikely to need to handle anything bigger than what off_t can handle; plus it leaves room for returning errors, although this particular function is not giving errors; see also Vladimir's work on making the block layer 64-bit clean). I'm not opposed to unsigned here to represent lack of errors, but consistency with the rest of the block layer may argue for signed. > +++ b/include/block/block_int.h > @@ -695,6 +695,13 @@ typedef struct BlockLimits { > * clamped down. */ > uint32_t max_transfer; > > + /* Maximal hardware transfer length in bytes. Applies whenever > + * transfers to the device bypass the kernel I/O scheduler, for > + * example with SG_IO. If larger than max_transfer or if zero, > + * blk_get_max_hw_transfer will fall back to max_transfer. > + */ > + uint64_t max_hw_transfer; > + Reviewed-by: Eric Blake <eblake@redhat.com>
On Tue, 2021-06-08 at 15:16 +0200, Paolo Bonzini wrote: > For block host devices, I/O can happen through either the kernel file > descriptor I/O system calls (preadv/pwritev, io_submit, io_uring) > or the SCSI passthrough ioctl SG_IO. > > In the latter case, the size of each transfer can be limited by the > HBA, while for file descriptor I/O the kernel is able to split and > merge I/O in smaller pieces as needed. Applying the HBA limits to > file descriptor I/O results in more system calls and suboptimal > performance, so this patch splits the max_transfer limit in two: > max_transfer remains valid and is used in general, while max_hw_transfer > is limited to the maximum hardware size. max_hw_transfer can then be > included by the scsi-generic driver in the block limits page, to ensure > that the stricter hardware limit is used. > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> This is mostly the same as my patch https://www.mail-archive.com/qemu-devel@nongnu.org/msg768264.html I called this max_ioctl_transfer, since this limit is only relevant to the .ioctl, but max_hw_transfer is fine as well. So this patch looks OK, but I might have missed something as I haven't touched this area for a long time. Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Best regards, Maxim Levitsky > --- > block/block-backend.c | 12 ++++++++++++ > block/file-posix.c | 2 +- > block/io.c | 1 + > hw/scsi/scsi-generic.c | 2 +- > include/block/block_int.h | 7 +++++++ > include/sysemu/block-backend.h | 1 + > 6 files changed, 23 insertions(+), 2 deletions(-) > > diff --git a/block/block-backend.c b/block/block-backend.c > index 15f1ea4288..2ea1412a54 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c > @@ -1953,6 +1953,18 @@ uint32_t blk_get_request_alignment(BlockBackend *blk) > return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE; > } > > +/* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero */ > +uint64_t blk_get_max_hw_transfer(BlockBackend *blk) > +{ > + BlockDriverState *bs = blk_bs(blk); > + uint64_t max = INT_MAX; > + > + if (bs) { > + max = MIN_NON_ZERO(bs->bl.max_hw_transfer, bs->bl.max_transfer); > + } > + return max; > +} > + > /* Returns the maximum transfer length, in bytes; guaranteed nonzero */ > uint32_t blk_get_max_transfer(BlockBackend *blk) > { > diff --git a/block/file-posix.c b/block/file-posix.c > index 670c577bfe..c9746d3eb6 100644 > --- a/block/file-posix.c > +++ b/block/file-posix.c > @@ -1234,7 +1234,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp) > int ret = sg_get_max_transfer_length(s->fd); > > if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) { > - bs->bl.max_transfer = pow2floor(ret); > + bs->bl.max_hw_transfer = pow2floor(ret); > } > > ret = sg_get_max_segments(s->fd); > diff --git a/block/io.c b/block/io.c > index 323854d063..089b99bb0c 100644 > --- a/block/io.c > +++ b/block/io.c > @@ -127,6 +127,7 @@ static void bdrv_merge_limits(BlockLimits *dst, const BlockLimits *src) > { > dst->opt_transfer = MAX(dst->opt_transfer, src->opt_transfer); > dst->max_transfer = MIN_NON_ZERO(dst->max_transfer, src->max_transfer); > + dst->max_hw_transfer = MIN_NON_ZERO(dst->max_hw_transfer, src->max_hw_transfer); > dst->opt_mem_alignment = MAX(dst->opt_mem_alignment, > src->opt_mem_alignment); > dst->min_mem_alignment = MAX(dst->min_mem_alignment, > diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c > index 82e1e2ee79..3762dce749 100644 > --- a/hw/scsi/scsi-generic.c > +++ b/hw/scsi/scsi-generic.c > @@ -179,7 +179,7 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s) > (r->req.cmd.buf[1] & 0x01)) { > page = r->req.cmd.buf[2]; > if (page == 0xb0) { > - uint32_t max_transfer = blk_get_max_transfer(s->conf.blk); > + uint64_t max_transfer = blk_get_max_hw_transfer(s->conf.blk); > uint32_t max_iov = blk_get_max_iov(s->conf.blk); > > assert(max_transfer); > diff --git a/include/block/block_int.h b/include/block/block_int.h > index 057d88b1fc..f1a54db0f8 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -695,6 +695,13 @@ typedef struct BlockLimits { > * clamped down. */ > uint32_t max_transfer; > > + /* Maximal hardware transfer length in bytes. Applies whenever > + * transfers to the device bypass the kernel I/O scheduler, for > + * example with SG_IO. If larger than max_transfer or if zero, > + * blk_get_max_hw_transfer will fall back to max_transfer. > + */ > + uint64_t max_hw_transfer; > + > /* memory alignment, in bytes so that no bounce buffer is needed */ > size_t min_mem_alignment; > > diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h > index 5423e3d9c6..9ac5f7bbd3 100644 > --- a/include/sysemu/block-backend.h > +++ b/include/sysemu/block-backend.h > @@ -208,6 +208,7 @@ void blk_eject(BlockBackend *blk, bool eject_flag); > int blk_get_flags(BlockBackend *blk); > uint32_t blk_get_request_alignment(BlockBackend *blk); > uint32_t blk_get_max_transfer(BlockBackend *blk); > +uint64_t blk_get_max_hw_transfer(BlockBackend *blk); > int blk_get_max_iov(BlockBackend *blk); > void blk_set_guest_block_size(BlockBackend *blk, int align); > void *blk_try_blockalign(BlockBackend *blk, size_t size);
diff --git a/block/block-backend.c b/block/block-backend.c index 15f1ea4288..2ea1412a54 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -1953,6 +1953,18 @@ uint32_t blk_get_request_alignment(BlockBackend *blk) return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE; } +/* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero */ +uint64_t blk_get_max_hw_transfer(BlockBackend *blk) +{ + BlockDriverState *bs = blk_bs(blk); + uint64_t max = INT_MAX; + + if (bs) { + max = MIN_NON_ZERO(bs->bl.max_hw_transfer, bs->bl.max_transfer); + } + return max; +} + /* Returns the maximum transfer length, in bytes; guaranteed nonzero */ uint32_t blk_get_max_transfer(BlockBackend *blk) { diff --git a/block/file-posix.c b/block/file-posix.c index 670c577bfe..c9746d3eb6 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -1234,7 +1234,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp) int ret = sg_get_max_transfer_length(s->fd); if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) { - bs->bl.max_transfer = pow2floor(ret); + bs->bl.max_hw_transfer = pow2floor(ret); } ret = sg_get_max_segments(s->fd); diff --git a/block/io.c b/block/io.c index 323854d063..089b99bb0c 100644 --- a/block/io.c +++ b/block/io.c @@ -127,6 +127,7 @@ static void bdrv_merge_limits(BlockLimits *dst, const BlockLimits *src) { dst->opt_transfer = MAX(dst->opt_transfer, src->opt_transfer); dst->max_transfer = MIN_NON_ZERO(dst->max_transfer, src->max_transfer); + dst->max_hw_transfer = MIN_NON_ZERO(dst->max_hw_transfer, src->max_hw_transfer); dst->opt_mem_alignment = MAX(dst->opt_mem_alignment, src->opt_mem_alignment); dst->min_mem_alignment = MAX(dst->min_mem_alignment, diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c index 82e1e2ee79..3762dce749 100644 --- a/hw/scsi/scsi-generic.c +++ b/hw/scsi/scsi-generic.c @@ -179,7 +179,7 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s) (r->req.cmd.buf[1] & 0x01)) { page = r->req.cmd.buf[2]; if (page == 0xb0) { - uint32_t max_transfer = blk_get_max_transfer(s->conf.blk); + uint64_t max_transfer = blk_get_max_hw_transfer(s->conf.blk); uint32_t max_iov = blk_get_max_iov(s->conf.blk); assert(max_transfer); diff --git a/include/block/block_int.h b/include/block/block_int.h index 057d88b1fc..f1a54db0f8 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -695,6 +695,13 @@ typedef struct BlockLimits { * clamped down. */ uint32_t max_transfer; + /* Maximal hardware transfer length in bytes. Applies whenever + * transfers to the device bypass the kernel I/O scheduler, for + * example with SG_IO. If larger than max_transfer or if zero, + * blk_get_max_hw_transfer will fall back to max_transfer. + */ + uint64_t max_hw_transfer; + /* memory alignment, in bytes so that no bounce buffer is needed */ size_t min_mem_alignment; diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h index 5423e3d9c6..9ac5f7bbd3 100644 --- a/include/sysemu/block-backend.h +++ b/include/sysemu/block-backend.h @@ -208,6 +208,7 @@ void blk_eject(BlockBackend *blk, bool eject_flag); int blk_get_flags(BlockBackend *blk); uint32_t blk_get_request_alignment(BlockBackend *blk); uint32_t blk_get_max_transfer(BlockBackend *blk); +uint64_t blk_get_max_hw_transfer(BlockBackend *blk); int blk_get_max_iov(BlockBackend *blk); void blk_set_guest_block_size(BlockBackend *blk, int align); void *blk_try_blockalign(BlockBackend *blk, size_t size);
For block host devices, I/O can happen through either the kernel file descriptor I/O system calls (preadv/pwritev, io_submit, io_uring) or the SCSI passthrough ioctl SG_IO. In the latter case, the size of each transfer can be limited by the HBA, while for file descriptor I/O the kernel is able to split and merge I/O in smaller pieces as needed. Applying the HBA limits to file descriptor I/O results in more system calls and suboptimal performance, so this patch splits the max_transfer limit in two: max_transfer remains valid and is used in general, while max_hw_transfer is limited to the maximum hardware size. max_hw_transfer can then be included by the scsi-generic driver in the block limits page, to ensure that the stricter hardware limit is used. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- block/block-backend.c | 12 ++++++++++++ block/file-posix.c | 2 +- block/io.c | 1 + hw/scsi/scsi-generic.c | 2 +- include/block/block_int.h | 7 +++++++ include/sysemu/block-backend.h | 1 + 6 files changed, 23 insertions(+), 2 deletions(-)