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Fri, 10 Apr 2026 17:27:29 +0000 Message-ID: <4fb7a6da-447d-452a-a920-7cd39b939ccb@intel.com> Date: Sat, 11 Apr 2026 01:27:14 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [Patch v4 02/22] sched/cache: Limit the scan number of CPUs when calculating task occupancy To: Tim Chen CC: Peter Zijlstra , K Prateek Nayak , Ingo Molnar , Vincent Guittot , Juri Lelli , "Dietmar Eggemann" , Steven Rostedt , Ben Segall , Mel Gorman , "Valentin Schneider" , Madadi Vineeth Reddy , Hillf Danton , Shrikanth Hegde , Jianyong Wu , Yangyu Chen , Tingyin Duan , Vern Hao , Vern Hao , Len Brown , Aubrey Li , Zhao Liu , Adam Li , Aaron Lu , Tim Chen , Josh Don , Gavin Guo , Qais Yousef , Libo Chen , , Luo Gengkun References: <57ed5fcec9b242803fe4ea2ce6e7f3de6a6efc6b.1775065312.git.tim.c.chen@linux.intel.com> <615986fc142de4c25a918083f6148752b1b341f1.camel@linux.intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <615986fc142de4c25a918083f6148752b1b341f1.camel@linux.intel.com> Content-Type: text/plain; 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>>>                 rq->cpu_runtime += delta_exec; >>>                 epoch = rq->cpu_epoch; >>> +               cpumask_set_cpu(cpu_of(rq), &mm->sc_stat.visited_cpus); >> >> I would refer a check before writing to avoid c2c overhead: >> if (!cpumask_test_cpu(cpu_of(rq), &mm->sc_stat.visited_cpus)) >> cpumask_set_cpu(cpu_of(rq), &mm->sc_stat.visited_cpus); > > > I think a similar check is also needed for clearing of visited CPU. It is possible that > the visited_cpus mask has already been cleared long time back. Change Yes, I agree, although we reach here when scanning the visited_cpus snapshot, there could be a race condition when we are in this loop but the CPU in visited_cpu has already been cleared. thanks, Chenyu > > + if (llc_epoch_visited_timeout && (rq->cpu_epoch - pcpu_sched->epoch) > > + llc_epoch_visited_timeout) { > + cpumask_clear_cpu(cpu_of(rq), &mm->sc_stat.visited_cpus); > + continue; > + } > > to > > + if (llc_epoch_visited_timeout && > + cpumask_test_cpu(cpu_of(rq), &mm->sc_stat.visitied_cpus) && > + (rq->cpu_epoch - pcpu_sched->epoch) > llc_epoch_visited_timeout) { > + cpumask_clear_cpu(cpu_of(rq), &mm->sc_stat.visited_cpus); > + continue; > + } > > Thanks. > > Tim > >