From: Chuanyu Qin <qinchuanyu@xxxxxxxxxx>
Subject: [PATCH] get 2% or more performance improved by reducing spin_lock race in vhost_work_queue
the wake_up_process func is included by spin_lock/unlock in vhost_work_queue,
but it could be done outside the spin_lock.
I have test it with kernel 3.0.27 and guest suse11-sp2 using iperf, the num as below.
orignal modified
thread_num tp(Gbps) vhost(%) | tp(Gbps) vhost(%)
1 9.59 28.82 | 9.59 27.49
8 9.61 32.92 | 9.62 26.77
64 9.58 46.48 | 9.55 38.99
256 9.6 63.7 | 9.6 52.59
Signed-off-by: Chuanyu Qin <qinchuanyu@xxxxxxxxxx>
---
drivers/vhost/vhost.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 94dbd25..8bee109 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -146,9 +146,10 @@ static inline void vhost_work_queue(struct vhost_dev *dev,
if (list_empty(&work->node)) {
list_add_tail(&work->node, &dev->work_list);
work->queue_seq++;
+ spin_unlock_irqrestore(&dev->work_lock, flags);
wake_up_process(dev->worker);
- }
- spin_unlock_irqrestore(&dev->work_lock, flags);
+ } else
+ spin_unlock_irqrestore(&dev->work_lock, flags);
}
void vhost_poll_queue(struct vhost_poll *poll)
--
1.7.3.1.msysgit.0
> On 05/20/2013 12:22 PM, Qinchuanyu wrote:
> > The patch below is base on
> > https://git.kernel.org/cgit/linux/kernel/git/next/linux-
> next.git/tree/drivers/vhost/vhost.c?id=refs/tags/next-20130517
> >
> > Signed-off-by: Chuanyu Qin <qinchuanyu@xxxxxxxxxx>
> > --- a/drivers/vhost/vhost.c 2013-05-20 11:47:05.000000000 +0800
> > +++ b/drivers/vhost/vhost.c 2013-05-20 11:48:24.000000000 +0800
> > @@ -154,9 +154,10 @@
> > if (list_empty(&work->node)) {
> > list_add_tail(&work->node, &dev->work_list);
> > work->queue_seq++;
> > + spin_unlock_irqrestore(&dev->work_lock, flags);
> > wake_up_process(dev->worker);
> > - }
> > - spin_unlock_irqrestore(&dev->work_lock, flags);
> > + } else
> > + spin_unlock_irqrestore(&dev->work_lock, flags);
> > }
> >
> > void vhost_poll_queue(struct vhost_poll *poll)
> >
> > I did the test by using iperf in 10G environment, the test num as
> below:
> > orignal modified
> > thread_num tp(Gbps) vhost(%) | tp(Gbps) vhost(%)
> > 1 9.59 28.82 | 9.59 27.49
> > 8 9.61 32.92 | 9.62 26.77
> > 64 9.58 46.48 | 9.55 38.99
> > 256 9.6 63.7 | 9.6 52.59
> >
> > The cost of vhost reduced while the throughput is almost unchanged.
>
> Thanks, and please generate a formal patch based on
> Documentation/SubmittingPatches (put the description and perf numbers
> in the commit log). Then resubmit it to let the maintainer apply it.
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