linux-kernel - Re: [PATCH-tip v3 11/11] locking/rwsem: Optimize rwsem structure for uncontended lock acquisition

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Message-ID: <a4daec7d-5e76-9e40-a4ed-522c6ccc89a4@redhat.com>
Date:   Wed, 3 Apr 2019 11:35:55 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH-tip v3 11/11] locking/rwsem: Optimize rwsem structure for
 uncontended lock acquisition

On 04/03/2019 09:12 AM, Peter Zijlstra wrote:
> On Thu, Feb 28, 2019 at 02:09:41PM -0500, Waiman Long wrote:
>> For an uncontended rwsem, count and owner are the only fields a task
>> needs to touch when acquiring the rwsem. So they are put next to each
>> other to increase the chance that they will share the same cacheline.
> Did you try and micro-bench this?
>
I haven't tried to micro-bench that as the one that I used will have
both owner and count in the same cacheline. I need to construct one with
all sort of different cacheline offfset to see if that makes a
difference. I will do so.

Thanks,
Longman