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authorPaolo Bonzini <pbonzini@redhat.com>2012-06-13 16:56:33 +0200
committerJames Bottomley <JBottomley@Parallels.com>2012-07-20 08:58:57 +0100
commitbce750b1633927be3eecf821f4d17975c3ba5b6a (patch)
treec2c02f7bb37c67e1f4e769b4eb064726e84fc0ac
parent139fe45abc2234b20fd5ecbcb7ea6d3688fed5e5 (diff)
downloadop-kernel-dev-bce750b1633927be3eecf821f4d17975c3ba5b6a.zip
op-kernel-dev-bce750b1633927be3eecf821f4d17975c3ba5b6a.tar.gz
[SCSI] virtio-scsi: release sg_lock after add_buf
We do not need the sglist after calling virtqueue_add_buf. Hence we can "pipeline" the locked operations and start preparing the sglist for the next request while we kick the virtqueue. Together with the previous two patches, this improves performance as follows. For a simple "if=/dev/sda of=/dev/null bs=128M iflag=direct" (the source being a 10G disk, residing entirely in the host buffer cache), the additional locking does not cause any penalty with only one dd process, but 2 simultaneous I/O operations improve their times by 3%: number of simultaneous dd 1 2 ---------------------------------------- current 5.9958s 10.2640s patched 5.9531s 9.8663s (Times are best of 10). Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: James Bottomley <JBottomley@Parallels.com>
-rw-r--r--drivers/scsi/virtio_scsi.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 0ecf95e..facfc90 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -281,11 +281,11 @@ static int virtscsi_kick_cmd(struct virtio_scsi *vscsi, struct virtio_scsi_vq *v
spin_lock(&vq->vq_lock);
ret = virtqueue_add_buf(vq->vq, vscsi->sg, out_num, in_num, cmd, gfp);
+ spin_unlock(&vscsi->sg_lock);
if (ret >= 0)
ret = virtqueue_kick_prepare(vq->vq);
- spin_unlock(&vq->vq_lock);
- spin_unlock_irqrestore(&vscsi->sg_lock, flags);
+ spin_unlock_irqrestore(&vq->vq_lock, flags);
if (ret > 0)
virtqueue_notify(vq->vq);
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