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

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Date:	Mon, 20 May 2013 03:06:25 +0000
From:	Qinchuanyu <qinchuanyu@...wei.com>
To:	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"mst@...hat.com" <mst@...hat.com>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>
CC:	" (kvm@...r.kernel.org)" <kvm@...r.kernel.org>,
	" (netdev@...r.kernel.org)" <netdev@...r.kernel.org>
Subject: [PATCH] vhost: get 2% performance improved by reducing spin_lock
 race in vhost_work_queue

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>
--- 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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