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Thu, 08 Jun 2023 03:32:17 -0700 (PDT) Date: Thu, 8 Jun 2023 18:32:10 +0800 From: Leo Yan To: James Clark Cc: coresight@lists.linaro.org, denik@chromium.org, Suzuki K Poulose , Mike Leach , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , John Garry , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/4] perf cs-etm: Use previous thread for branch sample source IP Message-ID: <20230608103210.GC123723@leoy-huanghe> References: <20230524131958.2139331-1-james.clark@arm.com> <20230524131958.2139331-3-james.clark@arm.com> <20230527090635.GB886420@leoy-yangtze.lan> <630ab636-107d-4b12-5454-2ee91ad43543@arm.com> <1e7aa657-6d1e-9e7c-95cb-b32d307abe93@arm.com> <20230608102555.GB123723@leoy-huanghe> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230608102555.GB123723@leoy-huanghe> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230608_033219_598509_28D3BED4 X-CRM114-Status: GOOD ( 18.64 ) 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 Thu, Jun 08, 2023 at 06:25:55PM +0800, Leo Yan wrote: [...] > Seems to me, this is a synchronization issue between the field > 'tidq->prev_thread' and 'tidq->prev_packet'. > > It's still hard for me to understand "two adjacent packets on the same > thread will say they branched from the previous thread that ran", IIUC, > even we move thread swapping into cs_etm__set_thread(), if the two > adjacent packets are in the same thread context, we can skip to update > fields 'tidq->prev_thread' and 'tidq->prev_packet'. Sorry for typo, here should be: ... skip to update fields 'tidq->prev_thread' and 'tidq->thread'. > So I am curious if below cs_etm__set_thread() works or not? > > static void cs_etm__set_thread(struct cs_etm_auxtrace *etm, > struct cs_etm_traceid_queue *tidq, pid_t tid) > { > struct machine *machine = &etm->session->machines.host; > > /* No context switching, bail out */ > if ((tidq->thread->tid != tid) > return; > > /* If tid is -1, we simply use idle thread context */ > if (tid == -1) > goto find_idle_thread; > > /* > * The new incoming tid is different from current thread, > * so it's to switch to the next thread context. > */ > > /* Swap thread contexts */ > thread__put(tidq->prev_thread); > tidq->prev_thread = thread__get(tidq->thread); > > /* Find thread context for new tid */ > thread__zput(tidq->thread); > tidq->thread = machine__find_thread(machine, -1, tid); > > find_idle_thread: > /* Couldn't find a known thread */ > if (!tidq->thread) > tidq->thread = machine__idle_thread(machine); > } > > Thanks, > Leo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel