Messages in this thread | | | Date | Mon, 9 Apr 2018 11:40:01 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 3/6] sched: Add over-utilization/tipping point indicator |
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(I know there is a new version out; but I was reading through this to catch up with the discussion)
On Tue, Mar 20, 2018 at 09:43:09AM +0000, Dietmar Eggemann wrote: > +static inline int sd_overutilized(struct sched_domain *sd) > +{ > + return READ_ONCE(sd->shared->overutilized); > +} > + > +static inline void update_overutilized_status(struct rq *rq) > +{ > + struct sched_domain *sd; > + > + rcu_read_lock(); > + sd = rcu_dereference(rq->sd); > + if (sd && !sd_overutilized(sd) && cpu_overutilized(rq->cpu)) > + WRITE_ONCE(sd->shared->overutilized, 1); > + rcu_read_unlock(); > +} > +#else
I think you ought to go have a look at the end of kernel/sched/topology.c:sd_init(), where it says:
/* * For all levels sharing cache; connect a sched_domain_shared * instance. */ if (sd->flags & SD_SHARE_PKG_RESOURCES) { sd->shared = *per_cpu_ptr(sdd->sds, sd_id); atomic_inc(&sd->shared->ref); atomic_set(&sd->shared->nr_busy_cpus, sd_weight); }
Because if I read all this correctly, your code assumes sd->shared exists unconditionally, while the quoted bit only ensures it does so <= LLC.
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