From: Peter Zijlstra <peterz@infradead.org>
To: "Liang, Kan" <kan.liang@intel.com>
Cc: "mingo@redhat.com" <mingo@redhat.com>,
"eranian@google.com" <eranian@google.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"alexander.shishkin@linux.intel.com"
<alexander.shishkin@linux.intel.com>,
"acme@redhat.com" <acme@redhat.com>,
"jolsa@redhat.com" <jolsa@redhat.com>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"vincent.weaver@maine.edu" <vincent.weaver@maine.edu>,
"ak@linux.intel.com" <ak@linux.intel.com>
Subject: Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter
Date: Mon, 22 May 2017 21:23:35 +0200 [thread overview]
Message-ID: <20170522192335.v4gvhz24ix2jeihg@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <37D7C6CF3E00A74B8858931C1DB2F077536F079F@SHSMSX103.ccr.corp.intel.com>
On Mon, May 22, 2017 at 04:55:47PM +0000, Liang, Kan wrote:
>
>
> > On Fri, May 19, 2017 at 10:06:21AM -0700, kan.liang@intel.com wrote:
> > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index
> > > 580b60f..e8b2326 100644
> > > --- a/arch/x86/events/core.c
> > > +++ b/arch/x86/events/core.c
> > > @@ -101,6 +101,10 @@ u64 x86_perf_event_update(struct perf_event
> > *event)
> > > delta = (new_raw_count << shift) - (prev_raw_count << shift);
> > > delta >>= shift;
> > >
> > > + /* Correct the count number if applying ref_cycles replacement */
> > > + if (!is_sampling_event(event) &&
> > > + (hwc->flags & PERF_X86_EVENT_REF_CYCLES_REP))
> > > + delta *= x86_pmu.ref_cycles_factor;
> >
> > That condition seems wrong, why only correct for !sampling events?
> >
>
> For sampling, it's either fixed freq mode or fixed period mode.
> - In the fixed freq mode, we should do nothing, because the adaptive
> frequency algorithm will handle it.
> - In the fixed period mode, we have already adjusted the period in
> ref_cycles_rep().
> Therefore, we should only handle !sampling events here.
How so? For sampling events the actual event count should also be
accurate.
next prev parent reply other threads:[~2017-05-22 19:23 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-19 17:06 [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter kan.liang
2017-05-19 17:06 ` [PATCH 2/2] perf/x86/intel, watchdog: Switch NMI watchdog to ref cycles on x86 kan.liang
2017-05-22 12:03 ` Peter Zijlstra
2017-05-22 12:04 ` Peter Zijlstra
2017-05-22 16:58 ` Liang, Kan
2017-05-22 19:24 ` Peter Zijlstra
2017-05-22 18:20 ` Stephane Eranian
2017-05-22 20:01 ` Andi Kleen
2017-05-22 8:30 ` [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Peter Zijlstra
2017-05-22 18:15 ` Stephane Eranian
2017-05-22 9:19 ` Peter Zijlstra
2017-05-22 12:22 ` Peter Zijlstra
2017-05-22 16:59 ` Liang, Kan
2017-05-22 16:55 ` Liang, Kan
2017-05-22 19:23 ` Peter Zijlstra [this message]
2017-05-22 19:28 ` Stephane Eranian
2017-05-22 21:51 ` Liang, Kan
2017-05-23 6:39 ` Peter Zijlstra
2017-05-23 6:42 ` Stephane Eranian
2017-05-24 15:45 ` Andi Kleen
2017-05-24 16:01 ` Vince Weaver
2017-05-24 16:55 ` Andi Kleen
2017-05-28 20:31 ` Stephane Eranian
2017-05-30 9:25 ` Peter Zijlstra
2017-05-30 13:51 ` Andi Kleen
2017-05-30 16:28 ` Peter Zijlstra
2017-05-30 16:41 ` Stephane Eranian
2017-05-30 17:22 ` Andi Kleen
2017-05-30 17:40 ` Peter Zijlstra
2017-05-30 17:51 ` Andi Kleen
2017-05-30 18:59 ` Peter Zijlstra
2017-05-30 19:40 ` Andi Kleen
2017-05-30 16:39 ` Stephane Eranian
2017-05-30 16:55 ` Thomas Gleixner
2017-05-30 17:25 ` Peter Zijlstra
2017-05-31 20:57 ` Vince Weaver
2017-05-28 2:56 ` kbuild test robot
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