lkml.org 
[lkml]   [2014]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] block: virtio_blk: don't hold spin lock during world switch
Date
Firstly, it isn't necessary to hold lock of vblk->vq_lock
when notifying hypervisor about queued I/O.

Secondly, virtqueue_notify() will cause world switch and
it may take long time on some hypervisors(such as, qemu-arm),
so it isn't good to hold the lock and block other vCPUs.

On arm64 quad core VM(qemu-kvm), the patch can increase I/O
performance a lot with VIRTIO_RING_F_EVENT_IDX enabled:
- without the patch: 14K IOPS
- with the patch: 34K IOPS

fio script:
[global]
direct=1
bsrange=4k-4k
timeout=10
numjobs=4
ioengine=libaio
iodepth=64

filename=/dev/vdc
group_reporting=1

[f1]
rw=randread

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
drivers/block/virtio_blk.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 9f340fa..a6f5424 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -162,6 +162,7 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
unsigned int num;
const bool last = (req->cmd_flags & REQ_END) != 0;
int err;
+ bool notify = false;

BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);

@@ -214,10 +215,12 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
return BLK_MQ_RQ_QUEUE_ERROR;
}

- if (last)
- virtqueue_kick(vblk->vq);
-
+ if (last && virtqueue_kick_prepare(vblk->vq))
+ notify = true;
spin_unlock_irqrestore(&vblk->vq_lock, flags);
+
+ if (notify)
+ virtqueue_notify(vblk->vq);
return BLK_MQ_RQ_QUEUE_OK;
}

--
1.7.9.5


\
 
 \ /
  Last update: 2014-05-30 05:21    [W:0.098 / U:0.124 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site