> > > So I changed it slightly to the below; changes are: > > - record 'lost' events to all set bits; after all we really do not > know which event this sample belonged to, only logging to the first > set bit seems 'wrong'.
If so, the same dropped sample will be count multiple times. It's hard to know the exact number of dropped samples. > > - dropped the @id field from the record, it is already included in the > @sample_id values. > --- > Subject: perf, x86: introduce PERF_RECORD_LOST_SAMPLES > From: Kan Liang <kan.li...@intel.com> > Date: Wed, 6 May 2015 15:33:53 -0400 > > After enlarging the PEBS interrupt threshold, there may be some mixed up > PEBS samples which are discarded by kernel. This patch drives the kernel to > emit a PERF_RECORD_LOST_SAMPLES record with the number of possible > discards when it is impossible to demux the samples. It makes sure the > user is not left in the dark about such discards. > > Cc: a...@infradead.org > Cc: eran...@google.com > Cc: a...@firstfloor.org > Cc: mi...@kernel.org > Signed-off-by: Kan Liang <kan.li...@intel.com> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> > Link: http://lkml.kernel.org/r/1430940834-8964-8-git-send-email- > kan.li...@intel.com > --- > arch/x86/kernel/cpu/perf_event_intel_ds.c | 22 ++++++++++++++++---- > include/linux/perf_event.h | 3 ++ > include/uapi/linux/perf_event.h | 12 ++++++++++ > kernel/events/core.c | 33 > ++++++++++++++++++++++++++++++ > 4 files changed, 66 insertions(+), 4 deletions(-) > > --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c > +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c > @@ -1124,8 +1124,9 @@ static void intel_pmu_drain_pebs_nhm(str > struct debug_store *ds = cpuc->ds; > struct perf_event *event; > void *base, *at, *top; > - int bit; > short counts[MAX_PEBS_EVENTS] = {}; > + short error[MAX_PEBS_EVENTS] = {}; > + int bit, i; > > if (!x86_pmu.pebs_active) > return; > @@ -1169,20 +1170,33 @@ static void intel_pmu_drain_pebs_nhm(str > /* slow path */ > pebs_status = p->status & cpuc->pebs_enabled; > pebs_status &= (1ULL << MAX_PEBS_EVENTS) - 1; > - if (pebs_status != (1 << bit)) > + if (pebs_status != (1 << bit)) { > + for (i = 0; 1 < MAX_PEBS_EVENTS; i++) { > + if (pebs_status & (1 << i)) > + error[i]++; > + } > continue; > + } > } > counts[bit]++; > } > > for (bit = 0; bit < x86_pmu.max_pebs_events; bit++) { > - if (counts[bit] == 0) > + if ((counts[bit] == 0) && (error[bit] == 0)) > continue; > + > event = cpuc->events[bit]; > WARN_ON_ONCE(!event); > WARN_ON_ONCE(!event->attr.precise_ip); > > - __intel_pmu_pebs_event(event, iregs, base, top, bit, > counts[bit]); > + /* log dropped samples number */ > + if (error[bit]) > + perf_log_lost_samples(event, error[bit]); > + > + if (counts[bit]) { > + __intel_pmu_pebs_event(event, iregs, base, > + top, bit, counts[bit]); > + } > } > } > > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -747,6 +747,9 @@ perf_event__output_id_sample(struct perf > struct perf_output_handle *handle, > struct perf_sample_data *sample); > > +extern void > +perf_log_lost_samples(struct perf_event *event, u64 lost); > + > static inline bool is_sampling_event(struct perf_event *event) { > return event->attr.sample_period != 0; > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -800,6 +800,18 @@ enum perf_event_type { > */ > PERF_RECORD_ITRACE_START = 12, > > + /* > + * Records the dropped/lost sample number. > + * > + * struct { > + * struct perf_event_header header; > + * > + * u64 lost; > + * struct sample_id sample_id; > + * }; > + */ > + PERF_RECORD_LOST_SAMPLES = 13, > + > PERF_RECORD_MAX, /* non-ABI */ > }; > > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -5947,6 +5947,39 @@ void perf_event_aux_event(struct perf_ev } > > /* > + * Lost/dropped samples logging > + */ > +void perf_log_lost_samples(struct perf_event *event, u64 lost) { > + struct perf_output_handle handle; > + struct perf_sample_data sample; > + int ret; > + > + struct { > + struct perf_event_header header; > + u64 lost; > + } lost_samples_event = { > + .header = { > + .type = PERF_RECORD_LOST_SAMPLES, > + .misc = 0, > + .size = sizeof(lost_samples_event), > + }, > + .lost = lost, > + }; > + > + perf_event_header__init_id(&lost_samples_event.header, > &sample, > +event); > + > + ret = perf_output_begin(&handle, event, > + lost_samples_event.header.size); > + if (ret) > + return; > + > + perf_output_put(&handle, lost_samples_event); > + perf_event__output_id_sample(event, &handle, &sample); > + perf_output_end(&handle); > +} > + > +/* > * IRQ throttle logging > */ > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org More majordomo > info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
