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Message-ID: <62bbdd77f70f7b46a044685668e33fb031812c38.camel@linux.intel.com>
Date: Wed, 26 Jan 2022 18:36:47 -0800
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Yicong Yang <yangyicong@...wei.com>,
Yicong Yang <yangyicong@...ilicon.com>, peterz@...radead.org,
mingo@...hat.com, juri.lelli@...hat.com,
vincent.guittot@...aro.org, gautham.shenoy@....com,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc: dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
bristot@...hat.com, prime.zeng@...wei.com,
jonathan.cameron@...wei.com, ego@...ux.vnet.ibm.com,
srikar@...ux.vnet.ibm.com, linuxarm@...wei.com, 21cnbao@...il.com,
song.bao.hua@...ilicon.com, guodong.xu@...aro.org
Subject: Re: [PATCH v2 2/2] sched/fair: Scan cluster before scanning LLC in
wake-up path
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@...ilicon.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@...ilicon.com>
> > > > Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> > > > Signed-off-by: Yicong Yang <yangyicong@...ilicon.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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