Messages in this thread | | | Subject | Re: [PATCH v2 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path | From | Tim Chen <> | Date | Wed, 26 Jan 2022 18:36:47 -0800 |
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On Wed, 2022-01-26 at 18:30 -0800, Tim Chen wrote: > On Thu, 2022-01-27 at 10:02 +0800, Yicong Yang wrote: > > On 2022/1/27 9:14, Tim Chen wrote: > > > On Wed, 2022-01-26 at 16:09 +0800, 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: > > > > 5.17-rc1 patched > > > > Hmean 1 324.73 ( 0.00%) 378.01 * 16.41%* > > > > Hmean 2 645.36 ( 0.00%) 754.63 * 16.93%* > > > > Hmean 4 1302.09 ( 0.00%) 1507.54 * 15.78%* > > > > Hmean 8 2612.03 ( 0.00%) 2982.57 * 14.19%* > > > > Hmean 16 5307.12 ( 0.00%) 5886.66 * 10.92%* > > > > Hmean 32 9354.22 ( 0.00%) 9908.13 * 5.92%* > > > > Hmean 64 7240.35 ( 0.00%) 7278.78 * 0.53%* > > > > Hmean 128 6186.40 ( 0.00%) 6187.85 ( 0.02%) > > > > > > > > On numa 0-1: > > > > 5.17-rc1 patched > > > > Hmean 1 320.01 ( 0.00%) 378.44 * 18.26%* > > > > Hmean 2 643.85 ( 0.00%) 752.52 * 16.88%* > > > > Hmean 4 1287.36 ( 0.00%) 1505.62 * 16.95%* > > > > Hmean 8 2564.60 ( 0.00%) 2955.29 * 15.23%* > > > > Hmean 16 5195.69 ( 0.00%) 5814.74 * 11.91%* > > > > Hmean 32 9769.16 ( 0.00%) 10872.63 * 11.30%* > > > > Hmean 64 15952.50 ( 0.00%) 17281.98 * 8.33%* > > > > Hmean 128 13113.77 ( 0.00%) 13895.20 * 5.96%* > > > > Hmean 256 10997.59 ( 0.00%) 11244.69 * 2.25%* > > > > Hmean 512 14623.60 ( 0.00%) 15526.25 * 6.17%* > > > > > > > > This will also help to improve the MySQL. With MySQL server > > > > running on numa 0 and client running on numa 1, both QPS and > > > > latency is imporved on read-write case: > > > > 5.17-rc1 patched > > > > QPS-16threads 143333.2633 145077.4033(+1.22%) > > > > QPS-24threads 195085.9367 202719.6133(+3.91%) > > > > QPS-32threads 241165.6867 249020.74(+3.26%) > > > > QPS-64threads 244586.8433 253387.7567(+3.60%) > > > > avg-lat-16threads 2.23 2.19(+1.19%) > > > > avg-lat-24threads 2.46 2.36(+3.79%) > > > > avg-lat-36threads 2.66 2.57(+3.26%) > > > > avg-lat-64threads 5.23 5.05(+3.44%) > > > > > > > > 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 | 46 > > > > +++++++++++++++++++++++++++++++++++++++++ > > > > ---- > > > > 1 file changed, 42 insertions(+), 4 deletions(-) > > > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > > index 5146163bfabb..2f84a933aedd 100644 > > > > --- a/kernel/sched/fair.c > > > > +++ b/kernel/sched/fair.c > > > > @@ -6262,12 +6262,46 @@ 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, int > > > > prev_cpu, > > > > int target) > > > > +{ > > > > + struct cpumask *cpus = > > > > this_cpu_cpumask_var_ptr(select_idle_mask); > > > > + struct sched_domain *sd = > > > > rcu_dereference(per_cpu(sd_cluster, > > > > target)); > > > > + int cpu, idle_cpu; > > > > + > > > > + /* TODO: Support SMT case while a machine with both > > > > cluster and > > > > SMT born */ > > > > > > This is probably a clearer comment > > > > > > /* TODO: Support SMT system with cluster topology */ > > > > > > > + if (!sched_smt_active() && sd) { > > > > + for_each_cpu_and(cpu, cpus, > > > > sched_domain_span(sd)) { > > > > + idle_cpu = __select_idle_cpu(cpu, p); > > > > */ > > > > -static int select_idle_cpu(struct task_struct *p, struct > > > > sched_domain *sd, bool has_idle_core, int target) > > > > +static int select_idle_cpu(struct task_struct *p, struct > > > > sched_domain *sd, bool has_idle_core, int prev_cpu, int target) > > > > { > > > > struct cpumask *cpus = > > > > this_cpu_cpumask_var_ptr(select_idle_mask); > > > > int i, cpu, idle_cpu = -1, nr = INT_MAX; > > > > @@ -6282,6 +6316,10 @@ static int select_idle_cpu(struct > > > > task_struct > > > > *p, struct sched_domain *sd, bool > > > > > > > > cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); > > > > > > > > + idle_cpu = scan_cluster(p, prev_cpu, target); > > > > > > Shouldn't "cpus" from > > > > > > cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); > > > > > > be passed to scan_cluster, to make sure that the cpu returned is > > > in the affinity mask of the task? I don't see p->cpus_ptr > > > being checked in scan_cluster to make sure the cpu found is in > > > the > > > affinity mask. > > > > > > > The cpus scanned in scan_cluster() is the intersection of > > select_idle_mask and sched_domain_span(cluster_sd), and > > we limited the select_idle_mask in the tasks' affinity mask > > before we enter scan_cluster() here. > > Ah, I missed the fact that cpus point to the select_idle_mask. >
I think it will be easier to read the code if you pass "cpus" directly to scan cluster, rather than making this implicit, and having this assignment
*cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
again in scan_cluster.
Tim
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