Messages in this thread | | | Date | Thu, 5 May 2022 20:44:16 +0200 | Subject | Re: [PATCH v8 1/7] sched/fair: Provide u64 read for 32-bits arch helper | From | Dietmar Eggemann <> |
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+ vdonnefort@gmail.com - vincent.donnefort@arm.com
On 05/05/2022 20:25, Dietmar Eggemann wrote: > On 29/04/2022 16:11, Vincent Donnefort wrote: >> Introducing macro helpers u64_u32_{store,load}() to factorize lockless >> accesses to u64 variables for 32-bits architectures. >> >> Users are for now cfs_rq.min_vruntime and sched_avg.last_update_time. To >> accommodate the later where the copy lies outside of the structure >> (cfs_rq.last_udpate_time_copy instead of sched_avg.last_update_time_copy), >> use the _copy() version of those helpers. >> >> Those new helpers encapsulate smp_rmb() and smp_wmb() synchronization and >> therefore, have a small penalty in set_task_rq_fair() and init_cfs_rq(). > > ... but obviously only on 32bit machines. And for set_task_rq_fair() we > now do one smp_rmb per cfs_rq (prev and next), like we do one smp_wmb() > per cfs_rq in update_cfs_rq_load_avg(). > > [...] > >> @@ -3786,8 +3770,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) >> decayed |= __update_load_avg_cfs_rq(now, cfs_rq); >> >> #ifndef CONFIG_64BIT > > Can we not get rid of this last CONFIG_64BIT here? > >> - smp_wmb(); >> - cfs_rq->load_last_update_time_copy = sa->last_update_time; >> + u64_u32_store_copy(sa->last_update_time, >> + cfs_rq->last_update_time_copy, >> + sa->last_update_time); > > (sa->last_update_time = sa->last_update_time); should dissolve on 64bit. > >> #endif > > [...] > > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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