This is a note to let you know that I have just added a patch titled
block: virtio_blk: don't hold spin lock during world switch
to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue
This patch is scheduled to be released in version 3.13.11.5.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From 7e3901f7d16885eed2126c03feb1ad993d86f207 Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Date: Fri, 30 May 2014 10:49:29 +0800
Subject: block: virtio_blk: don't hold spin lock during world switch
commit e8edca6f7f92234202d6dd163c118ef495244d7c upstream.
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@xxxxxxxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Acked-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
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 9b734f2..53e3db6 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -159,6 +159,7 @@ 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);
@@ -211,10 +212,12 @@ 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;
}
--
1.9.1
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