netdev - Re: [PATCH] tun: do not put self in waitq if doing a nonblock read

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Message-Id: <20110609.002721.963829441380663942.davem@davemloft.net>
Date:	Thu, 09 Jun 2011 00:27:21 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	akong@...hat.com
Cc:	netdev@...r.kernel.org, jasowang@...hat.com, kvm@...r.kernel.org,
	mst@...hat.com
Subject: Re: [PATCH] tun: do not put self in waitq if doing a nonblock read

From: Amos Kong <akong@...hat.com>
Date: Thu, 09 Jun 2011 07:46:06 +0800

> Perf shows a relatively high rate (about 8%) race in
> spin_lock_irqsave() when doing netperf between external host and
> guest. It's mainly becuase the lock contention between the
> tun_do_read() and tun_xmit_skb(), so this patch do not put self into
> waitqueue to reduce this kind of race. After this patch, it drops to
> 4%.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Amos Kong <akong@...hat.com>

Applied, thanks.
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