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

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Date:	Sun, 6 Oct 2013 11:10:54 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Adrian Hunter <adrian.hunter@...el.com>, 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


* Peter Zijlstra <peterz@...radead.org> wrote:

> 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.

I'm fully with you, please zap the 'notsc' boot option - it's an ancient 
relic, if any box is still broken with the TSC on we want to hear about it 
and fix it!

Thanks,

	Ingo
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