Messages in this thread | | | Subject | Re: [PATCH v2 2/6] sched/deadline: Optimize dl_bw_cpus() | From | Dietmar Eggemann <> | Date | Fri, 1 May 2020 18:12:05 +0200 |
| |
On 30/04/2020 12:55, Pavan Kondeti wrote: > On Mon, Apr 27, 2020 at 10:37:05AM +0200, Dietmar Eggemann wrote:
[..]
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c >> index 504d2f51b0d6..4ae22bfc37ae 100644 >> --- a/kernel/sched/deadline.c >> +++ b/kernel/sched/deadline.c >> @@ -54,10 +54,16 @@ static inline struct dl_bw *dl_bw_of(int i) >> static inline int dl_bw_cpus(int i) >> { >> struct root_domain *rd = cpu_rq(i)->rd; >> - int cpus = 0; >> + int cpus; >> >> RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(), >> "sched RCU must be held"); >> + >> + if (cpumask_subset(rd->span, cpu_active_mask)) >> + return cpumask_weight(rd->span); >> + > > Looks good to me. This is a nice optimization. > >> + cpus = 0; >> + >> for_each_cpu_and(i, rd->span, cpu_active_mask) >> cpus++; >> > Do you know why this check is in place? Is it only to cover > the case of cpuset_cpu_inactive()->dl_cpu_busy()?
It should cover:
(1) Preventing CPU hp when DL detects a possible overflow w/o the CPU:
sched_cpu_deactivate() -> cpuset_cpu_inactive() -> dl_cpu_busy() -> dl_bw_cpus() [now replaced by dl_bw_capacity()].
(2) DL Admission Control in CPU HP:
__sched_setscheduler() -> sched_dl_overflow() -> dl_bw_cpus() [now + -> dl_bw_capacity()]
(3) In create/destroy exclusive cpusets scenarios (comment in set_cpus_allowed_dl(), although I wasn't able to provoke this so far:
do_set_cpus_allowed() -> p->sched_class->set_cpus_allowed() was never called when I ran a DL testcase and create/destroy exclusive cpusets at the same time?
| |