From bce750b1633927be3eecf821f4d17975c3ba5b6a Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 13 Jun 2012 16:56:33 +0200 Subject: [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 Signed-off-by: James Bottomley --- drivers/scsi/virtio_scsi.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'drivers/scsi') diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c index 0ecf95e214d3..facfc90ef005 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); -- cgit v1.2.3