Messages in this thread | | | Date | Tue, 14 Apr 2020 16:32:52 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 03/13] sched: Core-wide rq->lock |
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On Wed, Mar 04, 2020 at 04:59:53PM +0000, vpillai wrote: > +DEFINE_STATIC_KEY_FALSE(__sched_core_enabled); > + > +/* > + * The static-key + stop-machine variable are needed such that: > + * > + * spin_lock(rq_lockp(rq)); > + * ... > + * spin_unlock(rq_lockp(rq)); > + * > + * ends up locking and unlocking the _same_ lock, and all CPUs > + * always agree on what rq has what lock. > + * > + * XXX entirely possible to selectively enable cores, don't bother for now. > + */ > +static int __sched_core_stopper(void *data) > +{ > + bool enabled = !!(unsigned long)data; > + int cpu; > + > + for_each_online_cpu(cpu) > + cpu_rq(cpu)->core_enabled = enabled; > + > + return 0; > +} > + > +static DEFINE_MUTEX(sched_core_mutex); > +static int sched_core_count; > + > +static void __sched_core_enable(void) > +{ > + // XXX verify there are no cookie tasks (yet) > + > + static_branch_enable(&__sched_core_enabled); > + stop_machine(__sched_core_stopper, (void *)true, NULL); > +} > + > +static void __sched_core_disable(void) > +{ > + // XXX verify there are no cookie tasks (left) > + > + stop_machine(__sched_core_stopper, (void *)false, NULL); > + static_branch_disable(&__sched_core_enabled); > +}
> +static inline raw_spinlock_t *rq_lockp(struct rq *rq) > +{ > + if (sched_core_enabled(rq)) > + return &rq->core->__lock; > + > + return &rq->__lock; > +}
While reading all this again, I realized it's not too hard to get rid of stop-machine here.
void __raw_rq_lock(struct rq *rq) { raw_spinlock_t *lock;
for (;;) { lock = rq_lockp(rq);
raw_spin_lock(lock); if (lock == rq_lock(rq)) return; raw_spin_unlock(lock); } }
void __sched_core_enable(int core, bool enable) { const cpumask *smt_mask; int cpu, i;
smt_mask = cpu_smt_mask(core);
for_each_cpu(cpu, smt_mask) raw_spin_lock_nested(&cpu_rq(cpu)->__lock, i++);
for_each_cpu(cpu, smt_mask) cpu_rq(cpu)->core_enabled = enable;
for_each_cpu(cpu, smt_mask) raw_spin_unlock(&cpu_rq(cpu)->__lock); }
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