From: Jason Wang <jasowang@redhat.com>
Date: Mon, 2 Sep 2013 08:40:57 +0000 (+0800)
Subject: vhost_net: use vhost_add_used_and_signal_n() in vhost_zerocopy_signal_used()
X-Git-Tag: v3.12-rc1~132^2~63
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c92112aed3f0b14fdd2dbd9f192cce1af22c0e1c;p=pandora-kernel.git

vhost_net: use vhost_add_used_and_signal_n() in vhost_zerocopy_signal_used()

We tend to batch the used adding and signaling in vhost_zerocopy_callback()
which may result more than 100 used buffers to be updated in
vhost_zerocopy_signal_used() in some cases. So switch to use
vhost_add_used_and_signal_n() to avoid multiple calls to
vhost_add_used_and_signal(). Which means much less times of used index
updating and memory barriers.

2% performance improvement were seen on netperf TCP_RR test.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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