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Tue, 27 Apr 2021 09:04:55 -0700 (PDT) Received: from leoy-ThinkPad-X240s ([204.124.180.30]) by smtp.gmail.com with ESMTPSA id t19sm2628853pjs.1.2021.04.27.09.04.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Apr 2021 09:04:54 -0700 (PDT) Date: Wed, 28 Apr 2021 00:04:43 +0800 From: Leo Yan To: Mathieu Poirier Cc: Mike Leach , "coresight@lists.linaro.org" , "denik@google.com" , "linux-arm-kernel@lists.infradead.org" , Daniel Kiss Subject: Re: [PATCH 0/4] coresight: Add ETR-PERF polling. Message-ID: <20210427160443.GA208852@leoy-ThinkPad-X240s> References: <20210421120413.3110775-1-daniel.kiss@arm.com> <20210426175425.GA1391779@xps15> <20210427154746.GA1422814@xps15> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210427154746.GA1422814@xps15> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210427_090456_612631_336D67E7 X-CRM114-Status: GOOD ( 16.29 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Apr 27, 2021 at 09:47:46AM -0600, Mathieu Poirier wrote: [...] > > 2) ETR polling ensures that more trace is collected across the entire > > trace session - seeking to reduce inconsistent capture volumes. > > I am not convinced disabling a sink to collect traces while an > event is active is the right way to go. To me it will add (more) complexity to > the coresight subsystem for very little gains, if any. > > If I remember correctly Leo brought forward the exact same idea about a year ago > and after discussion, we all agreed the benefit would not be important enough to > offset the drawbacks. > > As usual I am open to discussion and my opinion is not set in stone. But as I > mentioned I worry the feature will increase complexity in the driver and > produce dubious results. And we also have to factor in usability which, as > Al pointed, out will be a problem. Just want to remind one thing for ETR polling. From one perspective, the ETR polling mode is actually very similar with perf's snapshot mode. E.g. we can use specific interval to send USR2 singal to perf tool to captcure CoreSight trace data, thus it also can record the trace data continuously. I can see a benefit from ETR polling mode is it might introduce less overhead than perf snapshot mode. The kernel's mechanism (workqueue or kernel thread) will be much efficiency than perf's signal handling + SMP call with IPIs. So it's good to firstly understand if perf snapshot mode can meet the requirement or not. Thanks, Leo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel