Messages in this thread | | | Date | Fri, 21 Oct 2022 12:30:56 +0800 | Subject | Re: [PATCH v6 3/4] sched/fair: Introduce SIS_CORE | From | Abel Wu <> |
| |
Hi Chen, thanks for your reviewing!
On 10/21/22 12:03 PM, Chen Yu wrote: > On 2022-10-19 at 20:28:58 +0800, Abel Wu wrote: > [cut] >> A major concern is the accuracy of the idle cpumask. A cpu present >> in the mask might not be idle any more, which is called the false >> positive cpu. Such cpus will negate lots of benefit this feature >> brings. The strategy against the false positives will be introduced >> in next patch. >> > I was thinking that, if patch[3/4] needs [4/4] to fix the false positives, > maybe SIS_CORE could be disabled by default in 3/4 but enabled > in 4/4? So this might facilicate git bisect in case of any regression > check?
Agreed. Will fix in next version.
> [cut] >> + * To honor the rule of CORE granule update, set this cpu to the LLC idle >> + * cpumask only if there is no cpu of this core showed up in the cpumask. >> + */ >> +static void update_idle_cpu(int cpu) >> +{ >> + struct sched_domain_shared *sds; >> + >> + if (!sched_feat(SIS_CORE)) >> + return; >> + >> + sds = rcu_dereference(per_cpu(sd_llc_shared, cpu)); >> + if (sds) { >> + struct cpumask *icpus = to_cpumask(sds->icpus); >> + >> + /* >> + * This is racy against clearing in select_idle_cpu(), >> + * and can lead to idle cpus miss the chance to be set to >> + * the idle cpumask, thus the idle cpus are temporarily >> + * out of reach in SIS domain scan. But it should be rare >> + * and we still have ILB to kick them working. >> + */ >> + if (!cpumask_intersects(cpu_smt_mask(cpu), icpus)) >> + cpumask_set_cpu(cpu, icpus); > Maybe I miss something, here we only set one CPU in the icpus, but > when we reach update_idle_cpu(), all SMT siblings of 'cpu' are idle, > is this intended for 'CORE granule update'?
The __update_idle_core() is called by all the cpus that need to go idle to update has_idle_core if necessary, and update_idle_cpu() is called before that check.
Thanks, Abel
| |