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X-OriginatorOrg: intel.com Hi Gengkun, thanks for the update, On 7/9/2026 9:00 PM, Luo Gengkun wrote: > +static unsigned long fraction_mm_sched(int cpu, > + struct mm_struct *mm) > { > + struct sched_cache_time *pcpu_sched = > + per_cpu_ptr(mm->sc_stat.pcpu_sched, cpu); > + struct rq *rq = cpu_rq(cpu); > + > guard(raw_spinlock_irqsave)(&rq->cpu_epoch_lock); > > + /* Skip the rq that has not been hit for a long time */ > + if ((rq->cpu_epoch - pcpu_sched->epoch_timeout) > llc_epoch_affinity_timeout) { > + cpumask_clear_cpu(cpu, &mm->sc_stat.visited_cpus); > + return 0; > + } > + I was wondering if there is a race condition in the scenario above: If the rq has just updated its cpu_epoch field, and the CPU subsequently remains idle, then rq->cpu_epoch stays unchanged. That is to say, a race could occur as follows: if CPU1 becomes idle, CPU2's task_cache_work() might compute rq->cpu_epoch - pcpu_sched->epoch_timeout == 0 and consequently fail to clear CPU1 from visit_cpus. CPU_1 CPU_2 ------------------------------------ --------------------------------- account_mm_sched(rq_X) set CPU1 in visited_cpus (idle: fair task runs here, CPU1.cpu_epoch frozen afterwards, pcpu_sched->epoch_timeout = CPU1.epoch) fraction_mm_sched() CPU1->cpu_epoch - pcpu_sched->epoch_timeout = 0 -> bit CPU1 not cleared __update_mm_sched() ->update cpu_epoch, too late I wonder if we should let __update_mm_sched() be invoked before if ((rq->cpu_epoch - pcpu_sched->epoch_timeout) > llc_epoch_affinity_timeout)? BTW, in your test data: sched_cache_scan: comm=redis-server pid=24660 scan=384 Is it because NUMA balancing is disabled on your platform that it has to scan all the CPUs? It would be helpful to know what the result would be with NUMA balancing enabled. I found some reports from sashiko here that are worth taking a look at: https://sashiko.dev/#/patchset/20260709130053.2749834-1-luogengkun2%40huawei.com thanks, Chenyu