This is a note to let you know that I've just added the patch titled
block: virtio_blk: don't hold spin lock during world switch
to the 3.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
block-virtio_blk-don-t-hold-spin-lock-during-world-switch.patch
and it can be found in the queue-3.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From e8edca6f7f92234202d6dd163c118ef495244d7c Mon Sep 17 00:00:00 2001
From: Ming Lei <[email protected]>
Date: Fri, 30 May 2014 10:49:29 +0800
Subject: block: virtio_blk: don't hold spin lock during world switch
From: Ming Lei <[email protected]>
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 <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: [email protected]
Signed-off-by: Ming Lei <[email protected]>
Acked-by: Rusty Russell <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/block/virtio_blk.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -159,6 +159,7 @@ static int virtio_queue_rq(struct blk_mq
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
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;
}
Patches currently in stable-queue which might be from [email protected] are
queue-3.15/block-virtio_blk-don-t-hold-spin-lock-during-world-switch.patch
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