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, 18 Jan 2018 08:30:30 -0500 |
| |
On 1/18/2018 4:49 AM, Jiri Olsa wrote: > On Tue, Jan 16, 2018 at 01:49:13PM -0500, Liang, Kan wrote: >> >> >> On 1/11/2018 10:45 AM, Jiri Olsa wrote: >>> On Thu, Jan 11, 2018 at 10:21:25AM -0500, Liang, Kan wrote: >>> >>> SNIP >>> >>>>> >>>>> 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. >>> >>> hum, pmu->read is also called for PERF_SAMPLE_READ for sample, >>> check perf_output_read >>> >>> for non sampling event you shouldn't be able to create PEBS >>> event, there's check in x86_pmu_hw_config >>> >>> I agree it does not save much, it just confused me while >>> I was reading the code, like why is this needed for all >>> events with precise_ip >>> >> >> >> Sorry for the late response. >> >> How about the patch as below? >> The patch will be split into two patches in V3. One is to introduce >> intel_pmu_large_pebs_read, the other is to introduce intel_pmu_read_event. >> >> Thanks, >> Kan >> >> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c >> index 731153a..1610a9d 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 (intel_pmu_large_pebs_read(event)) >> + return; > > should this be 'if (!intel_pmu_large_pebs_read(event))' >
NO. For large pebs, the event->count has been updated in drain_pebs(). So it doesn't need to do x86_perf_event_update() again.
Thanks, Kan
> but looks better for me without the precise_ip check > > thanks, > jirka >
| |