linux-kernel - [PATCH v1] perf cs-etm: Pass -1 as pid value for machine__set_current

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Message-Id: <20211113143540.53957-1-leo.yan@linaro.org>
Date:   Sat, 13 Nov 2021 22:35:40 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Leo Yan <leo.yan@...aro.org>
Subject: [PATCH v1] perf cs-etm: Pass -1 as pid value for machine__set_current_tid()

Currently, cs-etm passes the tid value for both tid and pid parameters
when calling machine__set_current_tid(), this can lead to confusion for
thread handling.  E.g. we arbitrarily pass the same value for pid and
tid, perf tool will be misled to consider it is a main thread (see
thread__main_thread()).

On the other hand, Perf tool only can retrieve tid from Arm CoreSight
context packet, and we have no chance to know pid (it maps to kernel's
task_struct::tgid) from hardware tracing data.  For this reason, this
patch passes -1 as pid for function machine__set_current_tid().

Signed-off-by: Leo Yan <leo.yan@...aro.org>
---
 tools/perf/util/cs-etm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index f323adb1af85..eed1a5930072 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -1118,7 +1118,7 @@ int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
 	if (cs_etm__get_cpu(trace_chan_id, &cpu) < 0)
 		return err;
 
-	err = machine__set_current_tid(etm->machine, cpu, tid, tid);
+	err = machine__set_current_tid(etm->machine, cpu, -1, tid);
 	if (err)
 		return err;
 
-- 
2.25.1