linux-kernel - Re: [tip:perf/core] perf/x86: Clean up cap_user

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Message-ID: <20131004185539.GT15690@laptop.programming.kicks-ass.net>
Date:	Fri, 4 Oct 2013 20:55:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/x86: Clean up cap_user_time* setting

On Fri, Oct 04, 2013 at 09:31:22PM +0300, Adrian Hunter wrote:
> On 4/10/2013 8:31 p.m., tip-bot for Peter Zijlstra wrote:
> >Commit-ID:  d8b11a0cbd1c66ce283eb9dabe0498dfa6483f32
> >Gitweb:     http://git.kernel.org/tip/d8b11a0cbd1c66ce283eb9dabe0498dfa6483f32
> >Author:     Peter Zijlstra <peterz@...radead.org>
> >AuthorDate: Thu, 3 Oct 2013 16:00:14 +0200
> >Committer:  Ingo Molnar <mingo@...nel.org>
> >CommitDate: Fri, 4 Oct 2013 09:58:55 +0200
> >
> >perf/x86: Clean up cap_user_time* setting
> >
> >Currently the cap_user_time_zero capability has different tests than
> >cap_user_time; even though they expose the exact same data.
> >
> >Switch from CONSTANT && NONSTOP to sched_clock_stable to also deal
> >with multi cabinet machines and drop the tsc_disabled() check.. non of
> >this will work sanely without tsc anyway.
> 
> Unfortunately in the case that TSC is disabled, sched_clock is still
> reported as stable, which means removing the tsc_disabled() check breaks
> the capability bit. e.g.

I'm wanting to hear from the x86 people on why we have this absurd knob
to begin with; but I'm tempted to simply disable all of perf if you
touch it.
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