perf/x86/intel: Introduce PERF_RECORD_LOST_SAMPLES

After enlarging the PEBS interrupt threshold, there may be some mixed up
PEBS samples which are discarded by the kernel.

This patch makes the kernel emit a PERF_RECORD_LOST_SAMPLES record with
the number of possible discarded records when it is impossible to demux
the samples.

It makes sure the user is not left in the dark about such discards.

Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@infradead.org
Cc: eranian@google.com
Link: http://lkml.kernel.org/r/1431285195-14269-8-git-send-email-kan.liang@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 17 insertions, 3 deletions

diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
index 266079a3a646..34d0c4816141 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
@@ -1126,6 +1126,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs)
 	void *base, *at, *top;
 	int bit;
 	short counts[MAX_PEBS_EVENTS] = {};
+	short error[MAX_PEBS_EVENTS] = {};
 
 	if (!x86_pmu.pebs_active)
 		return;
@@ -1169,20 +1170,33 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs)
 			/* 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)) {
+				u8 i;
+
+				for_each_set_bit(i, (unsigned long *)&pebs_status,
+						 MAX_PEBS_EVENTS)
+					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]);
+		}
 	}
 }