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Date: Wed, 22 Dec 2021 14:26:53 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Yicong Yang <yangyicong@...ilicon.com>
Cc: peterz@...radead.org, mingo@...hat.com, juri.lelli@...hat.com,
tim.c.chen@...ux.intel.com, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, 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 2/2] sched/fair: Scan cluster before scanning LLC in
wake-up path
On Wed, 15 Dec 2021 at 05:11, Yicong Yang <yangyicong@...ilicon.com> 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. 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:
> 5.16-rc1 patched
> Hmean 1 329.17 ( 0.00%) 384.84 * 16.91%*
> Hmean 2 654.09 ( 0.00%) 768.77 * 17.53%*
> Hmean 4 1321.41 ( 0.00%) 1538.10 * 16.40%*
> Hmean 8 2650.43 ( 0.00%) 3048.86 * 15.03%*
> Hmean 16 5322.37 ( 0.00%) 5975.20 * 12.27%*
> Hmean 32 10002.11 ( 0.00%) 10085.57 * 0.83%*
> Hmean 64 7910.39 ( 0.00%) 7936.37 * 0.33%*
> Hmean 128 6745.25 ( 0.00%) 6811.28 * 0.98%*
>
> On numa 0-1:
> 5.16-rc1 patched
> Hmean 1 326.61 ( 0.00%) 385.36 * 17.99%*
> Hmean 2 650.62 ( 0.00%) 770.57 * 18.44%*
> Hmean 4 1318.05 ( 0.00%) 1534.83 * 16.45%*
> Hmean 8 2621.50 ( 0.00%) 3030.10 * 15.59%*
> Hmean 16 5252.17 ( 0.00%) 6023.08 * 14.68%*
> Hmean 32 9829.30 ( 0.00%) 9856.33 * 0.28%*
> Hmean 64 12452.66 ( 0.00%) 17338.48 * 39.24%*
> Hmean 128 14181.24 ( 0.00%) 15025.24 * 5.95%*
> Hmean 256 12239.07 ( 0.00%) 13080.16 * 6.87%*
> Hmean 512 14297.00 ( 0.00%) 15063.76 * 5.36%*
>
> 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:
> 5.16-rc1 patched
> QPS-24threads 195327.48 202081.28(+3.46%)
> QPS-32threads 242039.4 247059.5(+2.07%)
> QPS-64threads 243024.52 254274.47(+4.63%)
> avg-lat-24threads 2.46 2.37(+3.66%)
> avg-lat-36threads 2.64 2.59(+1.89%)
> avg-lat-64threads 5.27 5.03(+4.55%)
>
> 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 6e476f6d9435..8a5795c78af8 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6230,12 +6230,46 @@ 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_cluster(target, prev_cpu))
> + return target;
> +
> + cpumask_andnot(cpus, cpus, sched_domain_span(sd));
> + }
> +
> + return -1;
> +}
> +#else
> +static inline int scan_cluster(struct task_struct *p, int prev_cpu, int target)
> +{
> + 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
> * average idle time for this rq (as found in rq->avg_idle).
> */
> -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;
> @@ -6250,6 +6284,10 @@ 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);
Why don't you do the above before calling select_idle_cpu() like for smt ?
> + if ((unsigned int)idle_cpu < nr_cpumask_bits)
> + return idle_cpu;
> +
> if (sched_feat(SIS_PROP) && !has_idle_core) {
> u64 avg_cost, avg_idle, span_avg;
> unsigned long now = jiffies;
> @@ -6384,7 +6422,7 @@ 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_cluster(prev, target) &&
This is misleading because cpus_share_cluster is meaningless for most of system
Then, you don't care at all of the llc if there is a cluster domain ?
> (available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
> asym_fits_capacity(task_util, prev))
> return prev;
> @@ -6408,7 +6446,7 @@ 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_cluster(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)) {
> @@ -6449,7 +6487,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
> }
> }
>
> - i = select_idle_cpu(p, sd, has_idle_core, target);
> + i = select_idle_cpu(p, sd, has_idle_core, prev, target);
> if ((unsigned)i < nr_cpumask_bits)
> return i;
>
> --
> 2.33.0
>
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