Messages in this thread |  | | Date | Mon, 9 Apr 2018 11:47:10 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 3/6] sched: Add over-utilization/tipping point indicator |
| |
On Mon, Apr 09, 2018 at 11:40:01AM +0200, Peter Zijlstra wrote: > > (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.
Argh, n/m, I should read the whole patch before commenting I suppose ;-)
|  |