Messages in this thread | | | Date | Thu, 27 Jan 2022 21:11:01 +0530 | From | "Gautham R. Shenoy" <> | Subject | Re: [PATCH v2 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path |
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On Wed, Jan 26, 2022 at 04:09:47PM +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 */ > + if (!sched_smt_active() && sd) { > + for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) { > + idle_cpu = __select_idle_cpu(cpu, p); > + if ((unsigned int)idle_cpu < nr_cpumask_bits) > + return idle_cpu; > + } > + > + /* Don't ping-pong tasks in and out cluster frequently */ > + if (cpus_share_resources(target, prev_cpu)) > + return target;
We reach here when there aren't any idle CPUs within the cluster. However there might be idle CPUs in the MC domain. Is a busy @target preferable to a potentially idle CPU within the larger domain ?
-- Thanks and Regards gautham.
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