From: Amos Kong <akong@redhat.com>
Date: Thu, 9 Jun 2011 07:27:10 +0000 (-0700)
Subject: tun: do not put self in waitq if doing a nonblock read
X-Git-Tag: v3.1-rc1~316^2~450^2~37
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=61a5ff15ebdab87887861a6b128b108404e4706d;p=pandora-kernel.git

tun: do not put self in waitq if doing a nonblock read

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@redhat.com>
Signed-off-by: Amos Kong <akong@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

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