From: Peter Zijlstra <peterz@infradead.org>
To: "Liang, Kan" <kan.liang@linux.intel.com>
Cc: mingo@redhat.com, acme@kernel.org, linux-kernel@vger.kernel.org,
tglx@linutronix.de, jolsa@redhat.com, eranian@google.com,
ak@linux.intel.com
Subject: Re: [PATCH 2/4] perf/x86/intel: fix event update for auto-reload
Date: Tue, 19 Dec 2017 23:07:09 +0100 [thread overview]
Message-ID: <20171219220709.sq7kwvg7l2ojltvr@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <c1867cd6-4326-7e72-69e3-582dbe4d3199@linux.intel.com>
On Tue, Dec 19, 2017 at 03:08:58PM -0500, Liang, Kan wrote:
> > This all looks very wrong... In auto reload we should never call
> > intel_pmu_save_and_restore() in the first place I think.
> >
> > Things like x86_perf_event_update() and x86_perf_event_set_period()
> > simply _cannot_ do the right thing when we auto reload the counter.
> >
>
> I think it should be OK to call it in first place.
> For x86_perf_event_update(), the reload_times will tell if it's auto reload.
> Both period_left and event->count are carefully recalculated for auto
> reload.
How does prev_count make sense when we've already reloaded a bunch of
times?
> For x86_perf_event_set_period(), there is nothing special needed for auto
> reload. The period is fixed. The period_left from x86_perf_event_update() is
> already handled.
Hurm.. I see. But rather than make an ever bigger trainwreck of things,
I'd rather you just write a special purpose intel_pmu_save_and_restart()
just for AUTO_RELOAD.
next prev parent reply other threads:[~2017-12-19 22:07 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-18 11:34 [PATCH 0/4] bug fix mmap read in large PEBS kan.liang
2017-12-18 11:34 ` [PATCH 1/4] perf/x86/intel: pass auto-reload information to event update kan.liang
2017-12-18 11:34 ` [PATCH 2/4] perf/x86/intel: fix event update for auto-reload kan.liang
2017-12-19 18:58 ` Peter Zijlstra
2017-12-19 20:08 ` Liang, Kan
2017-12-19 20:24 ` Liang, Kan
2017-12-19 22:07 ` Peter Zijlstra [this message]
2017-12-19 22:11 ` Andi Kleen
2017-12-19 23:25 ` Liang, Kan
2017-12-18 11:34 ` [PATCH 3/4] perf/x86: introduce read function for x86_pmu kan.liang
2017-12-18 11:34 ` [PATCH 4/4] perf/x86/intel: drain PEBS buffer in event read kan.liang
2017-12-19 19:02 ` Peter Zijlstra
2017-12-19 20:10 ` Liang, Kan
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