[PATCH] get 2% or more performance improved by reducing spin_lock race

[PATCH] get 2% or more performance improved by reducing spin_lock race

[Qinchuanyu]

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@huawei.com>
---
 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

Re: [PATCH] get 2% or more performance improved by reducing spin_lock race

[Jason Wang]

On 06/07/2013 03:31 PM, Qinchuanyu 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.
>                  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@huawei.com>
> ---
>  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)

Hi Chuanyu:

I believe you need a better name of the patch such as:

vhost: wake up worker outside spinlock

Re: [PATCH] get 2% or more performance improved by reducing spin_lock race

[Sergei Shtylyov]

Hello.

On 07-06-2013 11:31, Qinchuanyu 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.
>                   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

    Could you align your columns?

> Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com>
> ---
>   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);

    You should have {} in the *else* branch, if you have it in the *if* 
branch (and vice versa), according to Documentation/CodingStyle.

WBR, Sergei