Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 7 Apr 2021 12:24:35 +0200 | Subject | Re: [PATCH v3] sched/fair: bring back select_idle_smt, but differently |
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On Wed, 7 Apr 2021 at 12:19, Peter Zijlstra <peterz@infradead.org> wrote: > > On Wed, Apr 07, 2021 at 11:54:37AM +0200, Peter Zijlstra wrote: > > > Let me have another poke at it. > > Pretty much what you did, except I also did s/smt/has_idle_core/ and > fixed that @sd thing. > > Like so then?
Yes. Looks good to me
> > --- > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6038,11 +6038,9 @@ static inline bool test_idle_cores(int c > { > struct sched_domain_shared *sds; > > - if (static_branch_likely(&sched_smt_present)) { > - sds = rcu_dereference(per_cpu(sd_llc_shared, cpu)); > - if (sds) > - return READ_ONCE(sds->has_idle_cores); > - } > + sds = rcu_dereference(per_cpu(sd_llc_shared, cpu)); > + if (sds) > + return READ_ONCE(sds->has_idle_cores); > > return def; > } > @@ -6112,6 +6110,24 @@ static int select_idle_core(struct task_ > return -1; > } > > +/* > + * Scan the local SMT mask for idle CPUs. > + */ > +static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) > +{ > + int cpu; > + > + for_each_cpu(cpu, cpu_smt_mask(target)) { > + if (!cpumask_test_cpu(cpu, p->cpus_ptr) || > + !cpumask_test_cpu(cpu, sched_domain_span(sd))) > + continue; > + if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) > + return cpu; > + } > + > + return -1; > +} > + > #else /* CONFIG_SCHED_SMT */ > > static inline void set_idle_cores(int cpu, int val) > @@ -6128,6 +6144,11 @@ static inline int select_idle_core(struc > return __select_idle_cpu(core); > } > > +static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) > +{ > + return -1; > +} > + > #endif /* CONFIG_SCHED_SMT */ > > /* > @@ -6135,11 +6156,10 @@ static inline int select_idle_core(struc > * comparing the average scan cost (tracked in sd->avg_scan_cost) against the > * average idle time for this rq (as found in rq->avg_idle). > */ > -static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target) > +static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool has_idle_core, int target) > { > struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); > int i, cpu, idle_cpu = -1, nr = INT_MAX; > - bool smt = test_idle_cores(target, false); > int this = smp_processor_id(); > struct sched_domain *this_sd; > u64 time; > @@ -6150,7 +6170,7 @@ static int select_idle_cpu(struct task_s > > cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); > > - if (sched_feat(SIS_PROP) && !smt) { > + if (sched_feat(SIS_PROP) && !has_idle_core) { > u64 avg_cost, avg_idle, span_avg; > > /* > @@ -6170,7 +6190,7 @@ static int select_idle_cpu(struct task_s > } > > for_each_cpu_wrap(cpu, cpus, target) { > - if (smt) { > + if (has_idle_core) { > i = select_idle_core(p, cpu, cpus, &idle_cpu); > if ((unsigned int)i < nr_cpumask_bits) > return i; > @@ -6184,10 +6204,10 @@ static int select_idle_cpu(struct task_s > } > } > > - if (smt) > + if (has_idle_core) > set_idle_cores(this, false); > > - if (sched_feat(SIS_PROP) && !smt) { > + if (sched_feat(SIS_PROP) && !has_idle_core) { > time = cpu_clock(this) - time; > update_avg(&this_sd->avg_scan_cost, time); > } > @@ -6242,6 +6262,7 @@ static inline bool asym_fits_capacity(in > */ > static int select_idle_sibling(struct task_struct *p, int prev, int target) > { > + bool has_idle_core = false; > struct sched_domain *sd; > unsigned long task_util; > int i, recent_used_cpu; > @@ -6321,7 +6342,17 @@ static int select_idle_sibling(struct ta > if (!sd) > return target; > > - i = select_idle_cpu(p, sd, target); > + if (static_branch_likely(&sched_smt_present)) { > + has_idle_core = test_idle_cores(target, false); > + > + if (!has_idle_core && cpus_share_cache(prev, target)) { > + i = select_idle_smt(p, sd, prev); > + if ((unsigned int)i < nr_cpumask_bits) > + return i; > + } > + } > + > + i = select_idle_cpu(p, sd, has_idle_core, target); > if ((unsigned)i < nr_cpumask_bits) > return i; >
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