linux-kernel - [PATCH 2/2] perf cs-etm: Set time on synthesised samples to preserve ordering

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Message-Id: <20210414143919.12605-2-james.clark@arm.com>
Date:   Wed, 14 Apr 2021 17:39:19 +0300
From:   James Clark <james.clark@....com>
To:     coresight@...ts.linaro.org
Cc:     al.grant@....com, branislav.rankov@....com, denik@...omium.org,
        suzuki.poulose@....com, James Clark <james.clark@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] perf cs-etm: Set time on synthesised samples to preserve ordering

The following attribute is set when synthesising samples in
timed decoding mode:

    attr.sample_type |= PERF_SAMPLE_TIME;

This results in new samples that appear to have timestamps but
because we don't assign any timestamps to the samples, when the
resulting inject file is opened again, the synthesised samples
will be on the wrong side of the MMAP or COMM events.

For example this results in the samples being associated with
the perf binary, rather than the target of the record:

    perf record -e cs_etm/@..._etr0/u top
    perf inject -i perf.data -o perf.inject --itrace=i100il
    perf report -i perf.inject

Where 'Command' == perf should show as 'top':

    # Overhead  Command  Source Shared Object  Source Symbol           Target Symbol           Basic Block Cycles
    # ........  .......  ....................  ......................  ......................  ..................
    #
        31.08%  perf     [unknown]             [.] 0x000000000040c3f8  [.] 0x000000000040c3e8  -

If the perf.data file is opened directly with perf, without the
inject step, then this already works correctly because the
events are synthesised after the COMM and MMAP events and
no second sorting happens. Re-sorting only happens when opening
the perf.inject file for the second time so timestamps are
needed.

Using the timestamp from the AUX record mirrors the current
behaviour when opening directly with perf, because the events
are generated on the call to cs_etm__process_queues().

Signed-off-by: James Clark <james.clark@....com>
Co-developed-by: Al Grant <al.grant@....com>
Signed-off-by: Al Grant <al.grant@....com>
---
 tools/perf/util/cs-etm.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index c25da2ffa8f3..d0fa9dce47f1 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -54,6 +54,7 @@ struct cs_etm_auxtrace {
 	u8 sample_instructions;
 
 	int num_cpu;
+	u64 latest_kernel_timestamp;
 	u32 auxtrace_type;
 	u64 branches_sample_type;
 	u64 branches_id;
@@ -1192,6 +1193,8 @@ static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
 	event->sample.header.misc = cs_etm__cpu_mode(etmq, addr);
 	event->sample.header.size = sizeof(struct perf_event_header);
 
+	if (!etm->timeless_decoding)
+		sample.time = etm->latest_kernel_timestamp;
 	sample.ip = addr;
 	sample.pid = tidq->pid;
 	sample.tid = tidq->tid;
@@ -1248,6 +1251,8 @@ static int cs_etm__synth_branch_sample(struct cs_etm_queue *etmq,
 	event->sample.header.misc = cs_etm__cpu_mode(etmq, ip);
 	event->sample.header.size = sizeof(struct perf_event_header);
 
+	if (!etm->timeless_decoding)
+		sample.time = etm->latest_kernel_timestamp;
 	sample.ip = ip;
 	sample.pid = tidq->pid;
 	sample.tid = tidq->tid;
@@ -2412,9 +2417,10 @@ static int cs_etm__process_event(struct perf_session *session,
 	else if (event->header.type == PERF_RECORD_SWITCH_CPU_WIDE)
 		return cs_etm__process_switch_cpu_wide(etm, event);
 
-	if (!etm->timeless_decoding &&
-	    event->header.type == PERF_RECORD_AUX)
+	if (!etm->timeless_decoding && event->header.type == PERF_RECORD_AUX) {
+		etm->latest_kernel_timestamp = sample_kernel_timestamp;
 		return cs_etm__process_queues(etm);
+	}
 
 	return 0;
 }
-- 
2.28.0