netdev - Re: [PATCH] vhost: get 2% performance improved by reducing spin_lock race in vhost_work

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Date:	Mon, 20 May 2013 12:15:58 +0800
From:	Lei Li <matrixs.zero@...il.com>
To:	Qinchuanyu <qinchuanyu@...wei.com>
CC:	Jason Wang <jasowang@...hat.com>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"mst@...hat.com" <mst@...hat.com>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"(kvm@...r.kernel.org)" <kvm@...r.kernel.org>,
	"(netdev@...r.kernel.org)" <netdev@...r.kernel.org>
Subject: Re: [PATCH] vhost: get 2% performance improved by reducing spin_lock
 race in vhost_work_queue

On 05/20/2013 11:38 AM, Jason Wang wrote:
> On 05/20/2013 11:06 AM, Qinchuanyu wrote:
>> Right now the wake_up_process func is included in spin_lock/unlock, but it could be done outside the spin_lock.
>> I have test it with kernel 3.0.27 and guest suse11-sp2, it provide 2%-3% net performance improved.
>>
>> Signed-off-by: Chuanyu Qin <qinchuanyu@...wei.com>
> Make sense to me but need generate a patch against net-next.git or
> vhost.git in git.kernel.org.
>
> Btw. How did you test this? Care to share the perf numbers?

I wonder how did you get the performance improved number 2%?

>
> Thanks
>> mu
>> --- a/drivers/vhost/vhost.c     2013-05-20 10:36:30.000000000 +0800
>> +++ b/drivers/vhost/vhost.c     2013-05-20 10:36:54.000000000 +0800
>> @@ -144,9 +144,10 @@
>>          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)
>> --
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