linux-kernel - Re: [PATCH v2] locking/pvqspinlock: Relax cmpxchg's to improve performance on some archs

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Message-ID: <20170104094149.GD25813@worktop.programming.kicks-ass.net>
Date:   Wed, 4 Jan 2017 10:41:49 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Pan Xinhui <xinhui@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v2] locking/pvqspinlock: Relax cmpxchg's to improve
 performance on some archs

On Tue, Jan 03, 2017 at 05:07:54PM -0500, Waiman Long wrote:
> On 01/03/2017 11:18 AM, Peter Zijlstra wrote:
> > On Sun, Dec 25, 2016 at 03:26:01PM -0500, Waiman Long wrote:
> >> A number of cmpxchg calls in qspinlock_paravirt.h were replaced by more
> >> relaxed versions to improve performance on architectures that use LL/SC.
> > Claim without numbers ;-)
> 
> Well it is hard to produce actual numbers here as I don't have the setup
> to gather data.

Surely RHT has big PPC machines around? I know that getting to them is a
wee bit of a bother, but they should be available somewhere.