From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Eric B Munson <emunson@mgebm.net>
Cc: eranian@google.com, mingo@elte.hu, anton@samba.org,
linux-kernel@vger.kernel.org, paulus@samba.org, hbabu@us.ibm.com
Subject: Re: Oprofile Regression Caused by commit e5d1367f17ba6a6fed5fd8b74e4d5720923e0c25 on PPC
Date: Tue, 11 Oct 2011 09:44:55 +0200 [thread overview]
Message-ID: <1318319095.14400.54.camel@laptop> (raw)
In-Reply-To: <20111010233842.GC24583@mgebm.net>
On Mon, 2011-10-10 at 19:38 -0400, Eric B Munson wrote:
> On Fri, 07 Oct 2011, Eric B Munson wrote:
>
> > This commit seems to have caused a regression with oprofile. It is fairly easy
> > to trigger, simply run oprofile monitoring an event that will fire (something
> > frequent like CPU cycles) causes oprofile to fail saying that the PMU is in use.
> > If I disable CONFIG_CGROUP_PERF, everything goes back to working. I suspect the
> > problem is that the PMU is being initialized without being reserved for perf. I
> > am not yet sure of the right fix yet so if you have any suggestions I would
> > appreciate them.
> >
> > Eric
>
> This isn't the best description of the behavior we see, what happens is at some
> point in the profiling session the MMCR register is clobbered by
> perf_cgroup_switch() which calls perf_pmu_enable() without reserving the PMC
> hardware. When this happens oprofile stops counting. It doesn't happen each
> time so some runs show event counts that are reasonable, but it can also lead to
> event counts that are smaller than expected, or completely missing.
What kernel are you testing?
next prev parent reply other threads:[~2011-10-11 7:38 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-07 20:42 Oprofile Regression Caused by commit e5d1367f17ba6a6fed5fd8b74e4d5720923e0c25 on PPC Eric B Munson
2011-10-10 23:38 ` Eric B Munson
2011-10-11 7:44 ` Peter Zijlstra [this message]
2011-10-11 7:47 ` Stephane Eranian
2011-10-11 13:34 ` Eric B Munson
2011-10-11 13:35 ` Stephane Eranian
2011-10-11 13:32 ` Eric B Munson
2011-10-12 16:51 ` Eric B Munson
2011-10-12 20:37 ` Stephane Eranian
2011-10-12 22:20 ` Eric B Munson
2011-10-18 13:53 ` Eric B Munson
2011-10-18 14:43 ` Peter Zijlstra
2011-10-18 14:50 ` Stephane Eranian
2011-10-18 15:20 ` Eric B Munson
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