linux-kernel - [tip:perf/urgent] perf/x86/intel: Fix debug

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Date:   Tue, 18 Jul 2017 03:44:49 -0700
From:   tip-bot for Jiri Olsa <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     kan.liang@...el.com, tglx@...utronix.de,
        torvalds@...ux-foundation.org, a.p.zijlstra@...llo.nl,
        mingo@...nel.org, jolsa@...nel.org, hpa@...or.com,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        alexander.shishkin@...ux.intel.com
Subject: [tip:perf/urgent] perf/x86/intel: Fix debug_store reset field for
 freq events

Commit-ID:  b32fd2f3f667c8a94f2f6bc2fb88a607be8f3229
Gitweb:     http://git.kernel.org/tip/b32fd2f3f667c8a94f2f6bc2fb88a607be8f3229
Author:     Jiri Olsa <jolsa@...nel.org>
AuthorDate: Fri, 14 Jul 2017 18:35:51 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 18 Jul 2017 11:06:12 +0200

perf/x86/intel: Fix debug_store reset field for freq events

There's a bug in PEBs event enabling code, that prevents PEBS
freq events to work properly after non freq PEBS event was run.

freq events - perf_event_attr::freq set
              -F <freq> option of perf record

PEBS events - perf_event_attr::precise_ip > 0
              default for perf record

Like in following example with CPU 0 busy, we expect ~10000 samples
for following perf tool run:

  # perf record -F 10000 -C 0 sleep 1
  [ perf record: Woken up 2 times to write data ]
  [ perf record: Captured and wrote 0.640 MB perf.data (10031 samples) ]

Everything's fine, but once we run non freq PEBS event like:

  # perf record -c 10000 -C 0 sleep 1
  [ perf record: Woken up 4 times to write data ]
  [ perf record: Captured and wrote 1.053 MB perf.data (20061 samples) ]

the freq events start to fail like this:

  # perf record -F 10000 -C 0 sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.185 MB perf.data (40 samples) ]

The issue is in non freq PEBs event initialization of debug_store reset
field, which value is used to auto-reload the counter value after PEBS
event drain. This value is not being used for PEBS freq events, but once
we run non freq event it stays in debug_store data and screws the
sample_freq counting for PEBS freq events.

Setting the reset field to 0 for freq events.

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Kan Liang <kan.liang@...el.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20170714163551.19459-1-jolsa@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/events/intel/ds.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 2ca4d2d..6dc8a59 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -895,6 +895,8 @@ void intel_pmu_pebs_enable(struct perf_event *event)
 	if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) {
 		ds->pebs_event_reset[hwc->idx] =
 			(u64)(-hwc->sample_period) & x86_pmu.cntval_mask;
+	} else {
+		ds->pebs_event_reset[hwc->idx] = 0;
 	}
 }