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Groups > linux.kernel > #1289691
| From | Alexander Shishkin <alexander.shishkin@linux.intel.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering |
| Date | 2015-12-11 16:50 +0100 |
| Message-ID | <qEy7f-6pg-1@gated-at.bofh.it> (permalink) |
| References | <qEw5s-52w-11@gated-at.bofh.it> <qEw5s-52w-9@gated-at.bofh.it> <qExuz-69x-39@gated-at.bofh.it> <qExNU-6hd-21@gated-at.bofh.it> <qExXA-6lB-13@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Peter Zijlstra <peterz@infradead.org> writes:
> On Fri, Dec 11, 2015 at 05:27:22PM +0200, Alexander Shishkin wrote:
>> Peter Zijlstra <peterz@infradead.org> writes:
>>
>> > On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote:
>> >> +static int perf_event_itrace_filters_setup(struct perf_event *event)
>> >> +{
>> >> + int ret;
>> >> +
>> >> + /*
>> >> + * We can't use event_function_call() here, because that would
>> >> + * require ctx::mutex, but one of our callers is called with
>> >> + * mm::mmap_sem down, which would cause an inversion, see bullet
>> >> + * (2) in put_event().
>> >> + */
>> >> + do {
>> >> + if (READ_ONCE(event->state) != PERF_EVENT_STATE_ACTIVE) {
>> >> + ret = event->pmu->itrace_filter_setup(event);
>> >> + break;
>> >
>> > So this is tricky, if its not active it can be any moment, there is
>> > nothing serializing against that.
>>
>> Indeed. But we should be able to call pmu::itrace_filter_setup()
>> multiple times, so if after this we re-check that the event is still
>> inactive, we can return, otherwise proceed with the cross-call. Does
>> this make sense?
>
> Dunno, I worry :-)
>
> What if:
>
> if (READ_ONCE(event->state) != PERF_EVENT_STATE_ACTIVE) {
> // we were INACTIVE, but now the event gets scheduled in
> // on _another_ CPU
> event->pmu->itrace_filter_setup() := {
> if (event->state == PERF_EVENT_STATE_ACTIVE) {
> /* muck with hardware */
> }
> }
> }
>
> Here too I feel a strict validation vs programming split would make sense.
>
> We can always call the validation thing, we must not call the program
> thing !ACTIVE is a clear and simple rule.
Ah, but pmu::itrace_filter_setup() does not touch the hardware,
pmu::start() does. The former keeps an array of, say, MSR values ready
for programming in event::hw and the latter actually writes the MSRs. So
the above example should not be a problem.
So in a way validation and programming are split already. And PT, for
example, won't have it any other way, you can only program stuff into
the registers while tracing is disabled.
Regards,
--
Alex
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[PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 14:40 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 15:10 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Mark Rutland <mark.rutland@arm.com> - 2015-12-11 15:30 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:00 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 16:20 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 15:30 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:00 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 16:20 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:10 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 16:30 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:40 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 16:50 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 17:10 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 18:10 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:30 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:10 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:10 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 16:20 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:40 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 17:10 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:20 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 16:30 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 18:10 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 18:20 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 23:40 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 18:00 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-12-11 18:20 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Mathieu Poirier <mathieu.poirier@linaro.org> - 2015-12-11 19:20 +0100
Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering Peter Zijlstra <peterz@infradead.org> - 2015-12-11 23:50 +0100
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