linux-kernel - Re: [PATCH 03/10] perf/x86: Correct local vs remote sibling state

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Message-ID: <20150521141034.GT3644@twins.programming.kicks-ass.net>
Date:	Thu, 21 May 2015 16:10:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/10] perf/x86: Correct local vs remote sibling state

On Thu, May 21, 2015 at 06:31:25AM -0700, Stephane Eranian wrote:
> On Thu, May 21, 2015 at 4:17 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > For some obscure reason the current code accounts the current SMT
> > thread's state on the remote thread and reads the remote's state on
> > the local SMT thread.
> >
> > While internally consistent, and 'correct' its pointless confusion we
> > can do without.
> >
> > Flip them the right way around.
> >
> So you are changing the logic here from:
> 
>   * EXCLUSIVE: sibling counter measuring exclusive event
>   * SHARED   : sibling counter measuring non-exclusive event
>   * UNUSED   : sibling counter unused
> 
> to:
> 
>    * EXCLUSIVE: current thread is using an exclusive event
>    * SHARED: current thread is using a non-exclusive event
>    * UNUSED: current thread is not using this counter
> 
> I am okay with this just need to make sure there were no
> assumptions made about that. I will look.

Right; and when we construct the constraint mask we look at the other
one too. So both on the update and the read side I flipped things
around.

And that is really the only thing that matters, that you look at the
other sibling's thread state when constructing that mask. And that's
kept invariant.
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