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

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Message-ID: <64289b85-8d10-e969-b05e-36184b6d8335@redhat.com>
Date:   Thu, 5 Jan 2017 10:30:11 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 01/04/2017 04:41 AM, Peter Zijlstra wrote:
> 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.

Yes, RHT does have PPC machines around. It is just I don't have
experience dealing with those machines yet. I will try to run some test
and include the numbers in the next version of the patch.

Cheers,
Longman