From: Paolo Bonzini <pbonzini@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: paulmck@linux.vnet.ibm.com,
linux-kernel <linux-kernel@vger.kernel.org>,
kvm@vger.kernel.org, gleb@redhat.com
Subject: Re: [PATCH RFC] kvm: optimize out smp_mb using srcu_read_unlock
Date: Thu, 31 Oct 2013 12:14:15 +0100 [thread overview]
Message-ID: <52723B87.1050609@redhat.com> (raw)
In-Reply-To: <20131030190929.GA7153@redhat.com>
Il 30/10/2013 20:09, Michael S. Tsirkin ha scritto:
> 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().
>
> Unsurprisingly, the gain is small but measureable using the unit test
> microbenchmark:
> before
> vmcall 1407
> after
> vmcall 1357
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Across how many runs? Best or average or "all runs were in that
ballpark", :) and what's the minimum/maximum before and after the patch?
As you say the benefit is not surprising, but the experiments should be
documented properly.
Paolo
next prev parent reply other threads:[~2013-10-31 11:14 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-30 19:09 [PATCH RFC] kvm: optimize out smp_mb using srcu_read_unlock Michael S. Tsirkin
2013-10-30 20:15 ` Paul E. McKenney
2013-10-30 23:26 ` Michael S. Tsirkin
2013-10-31 4:56 ` Paul E. McKenney
2013-10-31 6:47 ` Gleb Natapov
2013-10-31 11:11 ` Paolo Bonzini
2013-10-31 12:28 ` Gleb Natapov
2013-10-31 13:57 ` Michael S. Tsirkin
2013-11-01 8:43 ` Paul E. McKenney
2013-10-31 11:14 ` Paolo Bonzini [this message]
2013-10-31 11:32 ` Michael S. Tsirkin
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