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Message-ID: <alpine.DEB.2.20.1703171035490.13039@macbook-air>
Date: Fri, 17 Mar 2017 10:37:48 -0400 (EDT)
From: Vince Weaver <vincent.weaver@...ne.edu>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: perf: negative time_enabled issue
On Tue, 14 Mar 2017, Vince Weaver wrote:
> So another obscure rdpmc problem, turned up by the PAPI regression tests.
>
> If you use rdpmc, and your event is attached measuring another process,
> and then you ENABLE/DISABLE/ENABLE/rdpmc the event
>
> somehow the userpg->time_enabled field gets a weird value and that
> completely confuses code expecting enabled!=running to mean multiplexing
> is happening.
Still working on this issue. It turns out it's not rdpmc specific, you
can see it with a regular read() too.
So far I've traced it back far enough to see that shadow_ctx_time is
ending up negative for some reason if you do an enable/disable/enable on
an event attached to another process. I'm trying to trace it back further
but it's a slow process.
Vince
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