linux-kernel - [tip:perf/core] perf intel-pt: Fix instructions sampling rate

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Date:   Sat, 18 May 2019 02:32:39 -0700
From:   tip-bot for Adrian Hunter <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     acme@...hat.com, adrian.hunter@...el.com, hpa@...or.com,
        tglx@...utronix.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
        jolsa@...hat.com
Subject: [tip:perf/core] perf intel-pt: Fix instructions sampling rate

Commit-ID:  7ba8fa20e26eb3c0c04d747f7fd2223694eac4d5
Gitweb:     https://git.kernel.org/tip/7ba8fa20e26eb3c0c04d747f7fd2223694eac4d5
Author:     Adrian Hunter <adrian.hunter@...el.com>
AuthorDate: Fri, 10 May 2019 15:41:41 +0300
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Thu, 16 May 2019 14:17:23 -0300

perf intel-pt: Fix instructions sampling rate

The timestamp used to determine if an instruction sample is made, is an
estimate based on the number of instructions since the last known
timestamp. A consequence is that it might go backwards, which results in
extra samples. Change it so that a sample is only made when the
timestamp goes forwards.

Note this does not affect a sampling period of 0 or sampling periods
specified as a count of instructions.

Example:

 Before:

 $ perf script --itrace=i10us
 ls 13812 [003] 2167315.222583:       3270 instructions:u:      7fac71e2e494 __GI___tunables_init+0xf4 (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:      30902 instructions:u:      7fac71e2da0f _dl_cache_libcmp+0x2f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:         10 instructions:u:      7fac71e2d9ff _dl_cache_libcmp+0x1f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:          8 instructions:u:      7fac71e2d9ea _dl_cache_libcmp+0xa (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:         14 instructions:u:      7fac71e2d9ea _dl_cache_libcmp+0xa (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:          6 instructions:u:      7fac71e2d9ff _dl_cache_libcmp+0x1f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:         14 instructions:u:      7fac71e2d9ff _dl_cache_libcmp+0x1f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:          4 instructions:u:      7fac71e2dab2 _dl_cache_libcmp+0xd2 (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222728:      16423 instructions:u:      7fac71e2477a _dl_map_object_deps+0x1ba (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222734:      12731 instructions:u:      7fac71e27938 _dl_name_match_p+0x68 (/lib/x86_64-linux-gnu/ld-2.28.so)
 ...

 After:
 $ perf script --itrace=i10us
 ls 13812 [003] 2167315.222583:       3270 instructions:u:      7fac71e2e494 __GI___tunables_init+0xf4 (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:      30902 instructions:u:      7fac71e2da0f _dl_cache_libcmp+0x2f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222728:      16479 instructions:u:      7fac71e2477a _dl_map_object_deps+0x1ba (/lib/x86_64-linux-gnu/ld-2.28.so)
 ...

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: stable@...r.kernel.org
Fixes: f4aa081949e7b ("perf tools: Add Intel PT decoder")
Link: http://lkml.kernel.org/r/20190510124143.27054-2-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/intel-pt-decoder/intel-pt-decoder.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
index 872fab163585..26dbf11e071a 100644
--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -888,16 +888,20 @@ static uint64_t intel_pt_next_period(struct intel_pt_decoder *decoder)
 	timestamp = decoder->timestamp + decoder->timestamp_insn_cnt;
 	masked_timestamp = timestamp & decoder->period_mask;
 	if (decoder->continuous_period) {
-		if (masked_timestamp != decoder->last_masked_timestamp)
+		if (masked_timestamp > decoder->last_masked_timestamp)
 			return 1;
 	} else {
 		timestamp += 1;
 		masked_timestamp = timestamp & decoder->period_mask;
-		if (masked_timestamp != decoder->last_masked_timestamp) {
+		if (masked_timestamp > decoder->last_masked_timestamp) {
 			decoder->last_masked_timestamp = masked_timestamp;
 			decoder->continuous_period = true;
 		}
 	}
+
+	if (masked_timestamp < decoder->last_masked_timestamp)
+		return decoder->period_ticks;
+
 	return decoder->period_ticks - (timestamp - masked_timestamp);
 }
 
@@ -926,7 +930,10 @@ static void intel_pt_sample_insn(struct intel_pt_decoder *decoder)
 	case INTEL_PT_PERIOD_TICKS:
 		timestamp = decoder->timestamp + decoder->timestamp_insn_cnt;
 		masked_timestamp = timestamp & decoder->period_mask;
-		decoder->last_masked_timestamp = masked_timestamp;
+		if (masked_timestamp > decoder->last_masked_timestamp)
+			decoder->last_masked_timestamp = masked_timestamp;
+		else
+			decoder->last_masked_timestamp += decoder->period_ticks;
 		break;
 	case INTEL_PT_PERIOD_NONE:
 	case INTEL_PT_PERIOD_MTC: