From: Peter Zijlstra <peterz@infradead.org>
To: "Liang, Kan" <kan.liang@intel.com>
Cc: Stephane Eranian <eranian@google.com>,
"mingo@redhat.com" <mingo@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
"ak@linux.intel.com" <ak@linux.intel.com>,
"Odzioba, Lukasz" <lukasz.odzioba@intel.com>
Subject: Re: [PATCH] perf/x86: fix event counter update issue
Date: Tue, 29 Nov 2016 20:32:01 +0100 [thread overview]
Message-ID: <20161129193201.GE3045@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <37D7C6CF3E00A74B8858931C1DB2F07750CA4225@SHSMSX103.ccr.corp.intel.com>
On Tue, Nov 29, 2016 at 07:07:25PM +0000, Liang, Kan wrote:
> > diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> > index a74a2dbc0180..cb8522290e6a 100644
> > --- a/arch/x86/events/intel/core.c
> > +++ b/arch/x86/events/intel/core.c
> > @@ -4034,7 +4034,7 @@ __init int intel_pmu_init(void)
> >
> > /* Support full width counters using alternative MSR range */
> > if (x86_pmu.intel_cap.full_width_write) {
> > - x86_pmu.max_period = x86_pmu.cntval_mask;
> > + x86_pmu.max_period = x86_pmu.cntval_mask >> 1;
> > x86_pmu.perfctr = MSR_IA32_PMC0;
> > pr_cont("full-width counters, ");
> > }
>
> It doesn't work.
> perf stat -x, -C1 -e cycles -- sudo taskset 0x2 ./loop 100000000000
> 18446743727217821696,,cycles,313837854019,100.00
>
> delta 0xffffff8000001803 new 0x1804 prev 0xffffff8000000001
>
> I guess we need at least x86_pmu.cntval_mask >> 2 to prevent
> the sign flag set.
Possible delta should be u64, as we know the counter cannot decrement.
next prev parent reply other threads:[~2016-11-29 19:32 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-28 19:26 [PATCH] perf/x86: fix event counter update issue kan.liang
2016-11-28 19:41 ` Stephane Eranian
2016-11-28 19:59 ` Liang, Kan
2016-11-28 20:18 ` Stephane Eranian
2016-11-28 20:23 ` Liang, Kan
2016-11-29 9:25 ` Peter Zijlstra
2016-11-29 14:46 ` Liang, Kan
2016-11-29 16:58 ` Peter Zijlstra
2016-11-29 17:06 ` Liang, Kan
2016-11-29 17:17 ` Peter Zijlstra
2016-11-29 17:20 ` Stephane Eranian
2016-11-29 17:30 ` Peter Zijlstra
2016-11-29 18:11 ` Stephane Eranian
2016-11-29 18:37 ` Andi Kleen
2016-11-29 19:07 ` Liang, Kan
2016-11-29 19:32 ` Peter Zijlstra [this message]
2016-11-29 20:33 ` Liang, Kan
2016-11-29 20:37 ` Stephane Eranian
2016-12-02 12:58 ` Odzioba, Lukasz
2016-12-05 10:25 ` Peter Zijlstra
2016-12-05 11:21 ` Odzioba, Lukasz
2017-02-22 14:49 ` Vince Weaver
2017-02-22 15:28 ` Liang, Kan
2017-02-22 19:18 ` Andi Kleen
2017-02-23 15:07 ` Vince Weaver
2017-02-23 16:14 ` Liang, Kan
2016-11-29 19:08 ` Odzioba, Lukasz
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