netdev - Re: [PATCH] vhost: wake up worker outside spin

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Date:	Fri, 7 Jun 2013 22:05:37 +0800
From:	Asias He <asias.hejun@...il.com>
To:	Qin Chuanyu <qinchuanyu@...wei.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>, KVM <kvm@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] vhost: wake up worker outside spin_lock

On Fri, Jun 7, 2013 at 9:50 PM, Qin Chuanyu <qinchuanyu@...wei.com> wrote:
> 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.
>                  original                 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@...wei.com>
> ---
>  drivers/vhost/vhost.c |    4 +++-
>
>  1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 94dbd25..dcc7a17 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -146,9 +146,11 @@ 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);
> +       } else {
> +               spin_unlock_irqrestore(&dev->work_lock, flags);
>         }
> -       spin_unlock_irqrestore(&dev->work_lock, flags);
>
>  }

Hmm,  this looks more clearer to me.

--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -156,14 +156,17 @@ EXPORT_SYMBOL_GPL(vhost_poll_flush);
 void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
 {
        unsigned long flags;
+       bool wakeup = false;

        spin_lock_irqsave(&dev->work_lock, flags);
        if (list_empty(&work->node)) {
                list_add_tail(&work->node, &dev->work_list);
                work->queue_seq++;
-               wake_up_process(dev->worker);
+               wakeup = true;
        }
        spin_unlock_irqrestore(&dev->work_lock, flags);
+       if (wakeup)
+               wake_up_process(dev->worker);
 }


>
>  void vhost_poll_queue(struct vhost_poll *poll)
> --
> 1.7.3.1.msysgit.0
>
>
> --
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--
Asias
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