linux-kernel - Re: [patch] perf wrong enabled time after attach/enable/enable

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Message-ID: <20170809163059.zyd4sgbuylrmhq3r@hirez.programming.kicks-ass.net>
Date:   Wed, 9 Aug 2017 18:30:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Stephane Eranian <eranian@...il.com>
Subject: Re: [patch] perf wrong enabled time after attach/enable/enable

On Fri, Aug 04, 2017 at 01:22:53PM +0200, Peter Zijlstra wrote:
> On Thu, Aug 03, 2017 at 02:07:53PM -0400, Vince Weaver wrote:
> > On Wed, 2 Aug 2017, Peter Zijlstra wrote:
> > 
> > > Playing with that test it really is the IOC_DISABLE while STOP'ed that
> > > messes things up.
> > > 
> > > Ah.. magic.. the below seems to fix things, hopefully it doesn't break
> > > anything else.
> > 
> > yes, I've tested this and it seems to fix things.
> 
> New version below.. is a bit different and should handle another case.
> I'll try and run more tests on it, because while it _SHOULD_ not trigger
> that WARN_ON_ONCE() you know how that goes..

And splat it goes.. turns out we can attach to a ctx when OFF (which
makes sense, they need to live someplace too).

In that case the IOC_ENABLE will again go through
__perf_event_enable_time() and recompute things.

I think I'll just remove the WARN_ON_ONCE(), and put in a comment.