Messages in this thread | | | Date | Sun, 26 Jun 2022 20:13:49 +0800 | Subject | Re: [PATCH v4 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path | From | Abel Wu <> |
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On 6/9/22 8:06 PM, Yicong Yang Wrote: > From: Barry Song <song.bao.hua@hisilicon.com> > > For platforms having clusters like Kunpeng920, CPUs within the same cluster > have lower latency when synchronizing and accessing shared resources like > cache. Thus, this patch tries to find an idle cpu within the cluster of the > target CPU before scanning the whole LLC to gain lower latency. > > Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so this patch > doesn't consider SMT for this moment. > > Testing has been done on Kunpeng920 by pinning tasks to one numa and two > numa. On Kunpeng920, Each numa has 8 clusters and each cluster has 4 CPUs. > > With this patch, We noticed enhancement on tbench within one numa or cross > two numa. > > On numa 0: > 5.19-rc1 patched > Hmean 1 350.27 ( 0.00%) 406.88 * 16.16%* > Hmean 2 702.01 ( 0.00%) 808.22 * 15.13%* > Hmean 4 1405.14 ( 0.00%) 1614.34 * 14.89%* > Hmean 8 2830.53 ( 0.00%) 3169.02 * 11.96%* > Hmean 16 5597.95 ( 0.00%) 6224.20 * 11.19%* > Hmean 32 10537.38 ( 0.00%) 10524.97 * -0.12%* > Hmean 64 8366.04 ( 0.00%) 8437.41 * 0.85%* > Hmean 128 7060.87 ( 0.00%) 7150.25 * 1.27%* > > On numa 0-1: > 5.19-rc1 patched > Hmean 1 346.11 ( 0.00%) 408.47 * 18.02%* > Hmean 2 693.34 ( 0.00%) 805.78 * 16.22%* > Hmean 4 1384.96 ( 0.00%) 1602.49 * 15.71%* > Hmean 8 2699.45 ( 0.00%) 3069.98 * 13.73%* > Hmean 16 5327.11 ( 0.00%) 5688.19 * 6.78%* > Hmean 32 10019.10 ( 0.00%) 11862.56 * 18.40%* > Hmean 64 13850.57 ( 0.00%) 17748.54 * 28.14%* > Hmean 128 12498.25 ( 0.00%) 15541.59 * 24.35%* > Hmean 256 11195.77 ( 0.00%) 13854.06 * 23.74%* > > Tested-by: Yicong Yang <yangyicong@hisilicon.com> > Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> > Signed-off-by: Yicong Yang <yangyicong@hisilicon.com> > --- > kernel/sched/fair.c | 44 +++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 41 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 77b2048a9326..6d173e196ad3 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6327,6 +6327,40 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd > > #endif /* CONFIG_SCHED_SMT */ > > +#ifdef CONFIG_SCHED_CLUSTER > +/* > + * Scan the cluster domain for idle CPUs and clear cluster cpumask after scanning > + */ > +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus, > + int target, int *nr) > +{ > + struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, target)); > + int cpu, idle_cpu; > + > + /* TODO: Support SMT system with cluster topology */ > + if (!sched_smt_active() && sd) { > + for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) { > + if (!--*nr) > + break;
return -1; :)
> + > + idle_cpu = __select_idle_cpu(cpu, p); > + if ((unsigned int)idle_cpu < nr_cpumask_bits) > + return idle_cpu; > + } > + > + cpumask_andnot(cpus, cpus, sched_domain_span(sd)); > + } > + > + return -1; > +} > +#else > +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus, > + int target, int *nr) > +{ > + return -1; > +} > +#endif > + > /* > * Scan the LLC domain for idle CPUs; this is dynamically regulated by > * comparing the average scan cost (tracked in sd->avg_scan_cost) against the > @@ -6375,6 +6409,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > time = cpu_clock(this); > } > > + idle_cpu = scan_cluster(p, cpus, target, &nr); > + if ((unsigned int)idle_cpu < nr_cpumask_bits) > + return idle_cpu; > + > for_each_cpu_wrap(cpu, cpus, target + 1) { > if (has_idle_core) { > i = select_idle_core(p, cpu, cpus, &idle_cpu); > @@ -6382,7 +6420,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > return i; > > } else { > - if (!--nr) > + if (--nr <= 0) > return -1; > idle_cpu = __select_idle_cpu(cpu, p); > if ((unsigned int)idle_cpu < nr_cpumask_bits) > @@ -6481,7 +6519,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) > /* > * If the previous CPU is cache affine and idle, don't be stupid: > */ > - if (prev != target && cpus_share_cache(prev, target) && > + if (prev != target && cpus_share_resources(prev, target) && > (available_idle_cpu(prev) || sched_idle_cpu(prev)) && > asym_fits_capacity(task_util, prev)) > return prev; > @@ -6507,7 +6545,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) > p->recent_used_cpu = prev; > if (recent_used_cpu != prev && > recent_used_cpu != target && > - cpus_share_cache(recent_used_cpu, target) && > + cpus_share_resources(recent_used_cpu, target) && > (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) && > cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) && > asym_fits_capacity(task_util, recent_used_cpu)) {
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