Messages in this thread | | | From | bsegall@google ... | Subject | Re: [PATCH 2/2 v3] sched: Rewrite per entity runnable load average tracking | Date | Wed, 16 Jul 2014 11:53:23 -0700 |
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Morten Rasmussen <morten.rasmussen@arm.com> writes:
> On Wed, Jul 16, 2014 at 02:50:47AM +0100, Yuyang Du wrote: > > [...] > >> +/* >> + * Update load_avg of the cfs_rq along with its own se. They should get >> + * synchronized: group se's load_avg is used for task_h_load calc, and >> + * group cfs_rq's load_avg is used for task_h_load (and update_cfs_share >> + * calc). >> + */ >> +static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) >> { >> - long old_contrib = se->avg.load_avg_contrib; >> + int decayed; >> >> - if (entity_is_task(se)) { >> - __update_task_entity_contrib(se); >> - } else { >> - __update_tg_runnable_avg(&se->avg, group_cfs_rq(se)); >> - __update_group_entity_contrib(se); >> + if (atomic_long_read(&cfs_rq->removed_load_avg)) { >> + long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0); >> + cfs_rq->avg.load_avg = subtract_until_zero(cfs_rq->avg.load_avg, r); >> + r *= LOAD_AVG_MAX; >> + cfs_rq->avg.load_sum = subtract_until_zero(cfs_rq->avg.load_sum, r); >> } >> >> - return se->avg.load_avg_contrib - old_contrib; >> -} >> + decayed = __update_load_avg(now, &cfs_rq->avg, cfs_rq->load.weight); >> +#ifndef CONFIG_64BIT >> + if (cfs_rq->avg.last_update_time != cfs_rq->load_last_update_time_copy) >> + sa_q->last_update_time_copy = sa_q->last_update_time; > > This doesn't build on 32 bit. You need: > > - sa_q->last_update_time_copy = sa_q->last_update_time; > + cfs_rq->load_last_update_time_copy = cfs_rq->avg.last_update_time; > > to make it build. But I'm not convinced that this synchronization is > right. > > First let me say that I'm not an expert on synchronization. It seems to > me that there is nothing preventing reordering of the writes in > __update_load_avg() which sets cfs_rq->avg.last_update_time and the > update of cfs_rq->avg.load_last_update_time_copy.
You're correct, this needs to be if(...) { smp_wmb(); copy = time; }, the same as update_min_vruntime.
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