| Message ID | 1434472419-148742-6-git-send-email-imammedo@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Jun 16, 2015 at 06:33:39PM +0200, Igor Mammedov wrote: > when translating descriptors they are typically less than > memory region that holds them and translated into 1 iov > enty, entry > so it's not nessesary to check remaining length > twice and calculate used length and next address > in such cases. > > so relace replace > a remaining length and 'size' increment branches > with a single remaining length check and execute > next iov steps only when it needed. it is needed > > It saves tiny 2% of translate_desc() execution time. a tiny > > Signed-off-by: Igor Mammedov <imammedo@redhat.com> > --- > PS: > I'm not sure if iov_size > 0 is always true, if it's not > then better to drop this patch. > --- > drivers/vhost/vhost.c | 21 +++++++++++++-------- > 1 file changed, 13 insertions(+), 8 deletions(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 68c1c88..84c457d 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -1111,12 +1111,8 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, > int ret = 0; > > mem = vq->memory; > - while ((u64)len > s) { > + do { > u64 size; > - if (unlikely(ret >= iov_size)) { > - ret = -ENOBUFS; > - break; > - } > reg = find_region(mem, addr, len, &vq->cached_reg); > if (unlikely(!reg)) { > ret = -EFAULT; > @@ -1124,13 +1120,22 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, > } > _iov = iov + ret; > size = reg->memory_size - addr + reg->guest_phys_addr; > - _iov->iov_len = min((u64)len - s, size); > _iov->iov_base = (void __user *)(unsigned long) > (reg->userspace_addr + addr - reg->guest_phys_addr); > + ++ret; > + if (likely((u64)len - s < size)) { > + _iov->iov_len = (u64)len - s; > + break; > + } > + > + if (unlikely(ret >= iov_size)) { > + ret = -ENOBUFS; > + break; > + } > + _iov->iov_len = size; > s += size; > addr += size; > - ++ret; > - } > + } while (1); > > return ret; > } > -- > 1.8.3.1 -- 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/vhost/vhost.c b/drivers/vhost/vhost.c index 68c1c88..84c457d 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1111,12 +1111,8 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, int ret = 0; mem = vq->memory; - while ((u64)len > s) { + do { u64 size; - if (unlikely(ret >= iov_size)) { - ret = -ENOBUFS; - break; - } reg = find_region(mem, addr, len, &vq->cached_reg); if (unlikely(!reg)) { ret = -EFAULT; @@ -1124,13 +1120,22 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, } _iov = iov + ret; size = reg->memory_size - addr + reg->guest_phys_addr; - _iov->iov_len = min((u64)len - s, size); _iov->iov_base = (void __user *)(unsigned long) (reg->userspace_addr + addr - reg->guest_phys_addr); + ++ret; + if (likely((u64)len - s < size)) { + _iov->iov_len = (u64)len - s; + break; + } + + if (unlikely(ret >= iov_size)) { + ret = -ENOBUFS; + break; + } + _iov->iov_len = size; s += size; addr += size; - ++ret; - } + } while (1); return ret; }
when translating descriptors they are typically less than memory region that holds them and translated into 1 iov enty, so it's not nessesary to check remaining length twice and calculate used length and next address in such cases. so relace a remaining length and 'size' increment branches with a single remaining length check and execute next iov steps only when it needed. It saves tiny 2% of translate_desc() execution time. Signed-off-by: Igor Mammedov <imammedo@redhat.com> --- PS: I'm not sure if iov_size > 0 is always true, if it's not then better to drop this patch. --- drivers/vhost/vhost.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-)