Messages in this thread | | | Subject | Re: [RESEND PATCH V2 3/4] perf/x86/intel: drain PEBS buffer in event read | From | "Liang, Kan" <> | Date | Thu, 11 Jan 2018 10:21:25 -0500 |
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On 1/11/2018 6:10 AM, Jiri Olsa wrote: > On Wed, Jan 10, 2018 at 09:31:56AM -0500, Liang, Kan wrote: >> >> >> On 1/10/2018 5:39 AM, Jiri Olsa wrote: >>> On Mon, Jan 08, 2018 at 07:15:15AM -0800, kan.liang@intel.com wrote: >>>> From: Kan Liang <kan.liang@linux.intel.com> >>>> >>>> When the PEBS interrupt threshold is larger than one, there is no way to >>>> get exact auto-reload times and value needed for event update unless >>>> flush the PEBS buffer. >>>> >>>> Drain the PEBS buffer in event read when large PEBS is enabled. >>>> >>>> For the threshold is one, even auto-reload is enabled, it doesn't need >>>> to be specially handled. Because auto-reload is only effect when event >>>> overflow. There is no overflow in event read. >>>> >>>> Signed-off-by: Kan Liang <kan.liang@linux.intel.com> >>>> --- >>>> arch/x86/events/intel/core.c | 9 +++++++++ >>>> arch/x86/events/intel/ds.c | 10 ++++++++++ >>>> arch/x86/events/perf_event.h | 2 ++ >>>> 3 files changed, 21 insertions(+) >>>> >>>> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c >>>> index 09c26a4..bdc35f8 100644 >>>> --- a/arch/x86/events/intel/core.c >>>> +++ b/arch/x86/events/intel/core.c >>>> @@ -2060,6 +2060,14 @@ static void intel_pmu_del_event(struct perf_event *event) >>>> intel_pmu_pebs_del(event); >>>> } >>>> +static void intel_pmu_read_event(struct perf_event *event) >>>> +{ >>>> + if (event->attr.precise_ip) >>>> + return intel_pmu_pebs_read(event); >>> >>> check for (event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD) >>> would be more accurate? >>> >> >> It will narrow down the events. >> But considering the readability, I think it would be better to use >> precise_ip.The exposed functions in ds.c should be generic functions for all >> PEBS events, not specific case. >> I think _AUTO_RELOAD looks too specific. > > hum, but the PEBS drain is specific just for > PERF_X86_EVENT_AUTO_RELOAD events, right?
Accurately, PEBS drain is specific for PERF_X86_EVENT_FREERUNNING here. PERF_X86_EVENT_FREERUNNING event must be _AUTO_RELOAD event. But in some cases, _AUTO_RELOAD event cannot be _FREERUNNING event.
Only the event which is both _FREERUNNING and _AUTO_RELOAD need to do PEBS drain in _read().
So it does the check in intel_pmu_pebs_read() + if (pebs_needs_sched_cb(cpuc)) + return intel_pmu_drain_pebs_buffer();
> > wrt readability maybe you could add function like:
The existing function pebs_needs_sched_cb() can do the check. We just need to expose it, and also the intel_pmu_drain_pebs_buffer().
But to be honest, I still cannot see a reason for that. It could save a call to intel_pmu_pebs_read(), but _read() is not critical path. It doesn't save much. Also, it has to expose two inline PEBS specific functions. I think exposing one PEBS generic function would be better here.
Thanks, Kan > bool pebs_drain_before_read(struct perf_event *event) > { > return event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD; > } > > thanks, > jirka >
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