From: Michael S. Tsirkin <mst@redhat.com>
Date: Mon, 4 Nov 2013 20:36:25 +0000 (+0200)
Subject: kvm: optimize out smp_mb after srcu_read_unlock
X-Git-Tag: v3.13-rc1~80^2~8
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=01b71917b55d28c09ade9fb8c683cf0d2aad1858;p=pandora-kernel.git

kvm: optimize out smp_mb after srcu_read_unlock

I noticed that srcu_read_lock/unlock both have a memory barrier,
so just by moving srcu_read_unlock earlier we can get rid of
one call to smp_mb() using smp_mb__after_srcu_read_unlock instead.

Unsurprisingly, the gain is small but measureable using the unit test
microbenchmark:
before
        vmcall in the ballpark of 1410 cycles
after
        vmcall in the ballpark of 1360 cycles

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
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