linux-kernel - [PATCH v1 6/7] perf arm-spe: Bail out if the trace is later than perf event

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Date:   Mon, 21 Dec 2020 16:35:56 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ian Rogers <irogers@...gle.com>,
        James Clark <james.clark@....com>,
        Dave Martin <Dave.Martin@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Leo Yan <leo.yan@...aro.org>
Subject: [PATCH v1 6/7] perf arm-spe: Bail out if the trace is later than perf event

It's possible that record in Arm SPE trace is later than perf event and
vice versa.  This asks to correlate the perf events and Arm SPE
synthesized events to be processed in the manner of correct timing.

To achieve the time ordering, this patch reverses the flow, it firstly
calls arm_spe_sample() and then calls arm_spe_decode().  By comparing
the timestamp value and detect the perf event is coming earlier than Arm
SPE trace data, it bails out from the decoding loop, the last record is
pushed into auxtrace stack and is deferred to generate sample.  To track
the timestamp, everytime it updates timestamp for the latest record.

Signed-off-by: Leo Yan <leo.yan@...aro.org>
---
 tools/perf/util/arm-spe.c | 37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
index 2b008b973387..6bf2e4ff5342 100644
--- a/tools/perf/util/arm-spe.c
+++ b/tools/perf/util/arm-spe.c
@@ -353,12 +353,36 @@ static int arm_spe_sample(struct arm_spe_queue *speq)
 static int arm_spe_run_decoder(struct arm_spe_queue *speq, u64 *timestamp)
 {
 	struct arm_spe *spe = speq->spe;
+	struct arm_spe_record *record;
 	int ret;
 
 	if (!spe->kernel_start)
 		spe->kernel_start = machine__kernel_start(spe->machine);
 
 	while (1) {
+		/*
+		 * The usual logic is firstly to decode the packets, and then
+		 * based the record to synthesize sample; but here the flow is
+		 * reversed: it calls arm_spe_sample() for synthesizing samples
+		 * prior to arm_spe_decode().
+		 *
+		 * Two reasons for this code logic:
+		 * 1. Firstly, when setup queue in arm_spe__setup_queue(), it
+		 * has decoded trace data and generated a record, but the record
+		 * is left to generate sample until run to here, so it's correct
+		 * to synthesize sample for the left record.
+		 * 2. After decoding trace data, it needs to compare the record
+		 * timestamp with the coming perf event, if the record timestamp
+		 * is later than the perf event, it needs bail out and pushs the
+		 * record into auxtrace heap, thus the record can be deferred to
+		 * synthesize sample until run to here at the next time; so this
+		 * can correlate samples between Arm SPE trace data and other
+		 * perf events with correct time ordering.
+		 */
+		ret = arm_spe_sample(speq);
+		if (ret)
+			return ret;
+
 		ret = arm_spe_decode(speq->decoder);
 		if (!ret) {
 			pr_debug("No data or all data has been processed.\n");
@@ -372,10 +396,17 @@ static int arm_spe_run_decoder(struct arm_spe_queue *speq, u64 *timestamp)
 		if (ret < 0)
 			continue;
 
-		ret = arm_spe_sample(speq);
-		if (ret)
-			return ret;
+		record = &speq->decoder->record;
 
+		/* Update timestamp for the last record */
+		if (record->timestamp > speq->timestamp)
+			speq->timestamp = record->timestamp;
+
+		/*
+		 * If the timestamp of the queue is later than timestamp of the
+		 * coming perf event, bail out so can allow the perf event to
+		 * be processed ahead.
+		 */
 		if (!spe->timeless_decoding && speq->timestamp >= *timestamp) {
 			*timestamp = speq->timestamp;
 			return 0;
-- 
2.17.1