linux-kernel - Re: [PATCH v2 02/11] locking/ww_mutex: Re-check ww->ctx in the inner optimistic spin loop

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Date:   Tue, 6 Dec 2016 13:46:42 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nicolai Hähnle <nhaehnle@...il.com>,
        linux-kernel@...r.kernel.org,
        Nicolai Hähnle <Nicolai.Haehnle@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Maarten Lankhorst <dev@...ankhorst.nl>,
        Daniel Vetter <daniel@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 02/11] locking/ww_mutex: Re-check ww->ctx in the inner
 optimistic spin loop

On 12/06/2016 01:29 PM, Peter Zijlstra wrote:
> On Tue, Dec 06, 2016 at 11:03:28AM -0500, Waiman Long wrote:
>> The mutex_spin_on_owner() function was originally marked noinline
>> because it could be a major consumer of CPU cycles in a contended lock.
>> Having it shown separately in the perf output will help the users have a
>> better understanding of what is consuming all the CPU cycles. So I would
>> still like to keep it this way.
> ah!, I tried to dig through history but couldn't find a reason for it.
>
>> If you have concern about additional latency for non-ww_mutex calls, one
>> alternative can be:
> That's pretty horrific :/

I am not totally against making mutex_spin_on_owner() an inline
function. If you think it is the right way to go, I am OK with that.

-Longman