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Date: Sun, 26 Jun 2022 20:13:49 +0800
From: Abel Wu <wuyun.abel@...edance.com>
To: Yicong Yang <yangyicong@...ilicon.com>, peterz@...radead.org,
mingo@...hat.com, juri.lelli@...hat.com,
vincent.guittot@...aro.org, tim.c.chen@...ux.intel.com,
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,
guodong.xu@...aro.org, hesham.almatary@...wei.com,
john.garry@...wei.com, shenyang39@...wei.com
Subject: Re: [PATCH v4 2/2] sched/fair: Scan cluster before scanning LLC in
wake-up path
On 6/9/22 8:06 PM, 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:
> 5.19-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@...ilicon.com>
> Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> Signed-off-by: Yicong Yang <yangyicong@...ilicon.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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