linux-kernel - Re: [tip:sched/core] perf/core, sched: Don't use clock function pointer to determine clock

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Date:	Wed, 20 Apr 2016 07:06:16 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	torvalds@...ux-foundation.org, tglx@...utronix.de, bp@...en8.de,
	peterz@...radead.org, alexander.shishkin@...ux.intel.com,
	linux-kernel@...r.kernel.org, mingo@...nel.org, acme@...radead.org,
	hpa@...or.com, a.p.zijlstra@...llo.nl
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] perf/core, sched: Don't use clock function
 pointer to determine clock

On Tue, Apr 19, 2016 at 02:34:50AM -0700, tip-bot for Alexander Shishkin wrote:
> Commit-ID:  f454bfddf6ba557381d8bf5df50eff778602ff23
> Gitweb:     http://git.kernel.org/tip/f454bfddf6ba557381d8bf5df50eff778602ff23
> Author:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> AuthorDate: Thu, 14 Apr 2016 14:59:49 +0300
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Tue, 19 Apr 2016 10:55:29 +0200
> 
> perf/core, sched: Don't use clock function pointer to determine clock
> 
> Now that local_clock() is explicitly inlined in sched.h, taking its
> pointer would uninline it in the compilation unit where it's done,
> making (among other things) comparing pointers to this function
> produce different results in different compilation units.
> 
> Case in point, x86 perf core's user page updating function compares
> event's clock against &local_clock to see if it needs to set zero
> time offset related bits in the page.
> 
> This patch fixes the latter by looking at the "use_clockid" event
> attribute instead, to determine whether local clock is used. Fixing
> the uninlined local_clock() in perf core is left as an exercise for
> the author of the prior work.

Ouch! Good exercise :)