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[68.147.0.187]) by smtp.gmail.com with ESMTPSA id f15sm212467pfe.171.2021.11.18.09.14.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Nov 2021 09:14:15 -0800 (PST) Date: Thu, 18 Nov 2021 10:14:12 -0700 From: Mathieu Poirier To: Leo Yan Cc: Arnaldo Carvalho de Melo , Namhyung Kim , Suzuki K Poulose , Mike Leach , John Garry , Will Deacon , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , linux-arm-kernel@lists.infradead.org, coresight@lists.linaro.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1] perf cs-etm: Pass -1 as pid value for machine__set_current_tid() Message-ID: <20211118171412.GB2530497@p14s> References: <20211113143540.53957-1-leo.yan@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211113143540.53957-1-leo.yan@linaro.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Good morning Leo, On Sat, Nov 13, 2021 at 10:35:40PM +0800, Leo Yan wrote: > 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 > --- > 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); I remember wondering about what to do with the pid parameter when I wrote this patch... Do you have a before-and-after snapshot you can add to the changelog? I also think it will require a "Fixes" tag. In your next revision please CC James since you guys are working in that area nowadays. Thanks, Mathieu > if (err) > return err; > > -- > 2.25.1 >