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Date: Wed, 20 Jul 2022 23:33:39 +1200
From: Barry Song <21cnbao@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Yicong Yang <yangyicong@...ilicon.com>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
"Gautham R. Shenoy" <gautham.shenoy@....com>,
LKML <linux-kernel@...r.kernel.org>,
LAK <linux-arm-kernel@...ts.infradead.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
prime.zeng@...wei.com,
Jonathan Cameron <jonathan.cameron@...wei.com>,
ego@...ux.vnet.ibm.com,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Linuxarm <linuxarm@...wei.com>,
Guodong Xu <guodong.xu@...aro.org>, hesham.almatary@...wei.com,
john.garry@...wei.com, Yang Shen <shenyang39@...wei.com>,
kprateek.nayak@....com, Chen Yu <yu.c.chen@...el.com>,
wuyun.abel@...edance.com
Subject: Re: [RESEND PATCH v5 2/2] sched/fair: Scan cluster before scanning
LLC in wake-up path
On Wed, Jul 20, 2022 at 11:15 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Jul 20, 2022 at 04:11:50PM +0800, Yicong Yang wrote:
> > + /* TODO: Support SMT system with cluster topology */
> > + if (!sched_smt_active() && sd) {
> > + for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
>
> So that's no SMT and no wrap iteration..
>
> Does something like this work?
I guess it is ok. The main reason for me to disable smt from the first beginning
is that we don't really have a machine with both cluster and smt to
reach the code
for smt, aka has_idle_core=true. so I thought I was going to bring up
that branch
when I really have a machine. so, it is marked as TODO.
till now, neither kunpeng920 nor Jacobsville is smt.
But I don't mind if it is enabled now.
>
> ---
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6437,6 +6437,30 @@ static int select_idle_cpu(struct task_s
> }
> }
>
> + if (IS_ENABLED(CONFIG_SCHED_CLUSTER) &&
> + static_branch_unlikely(&sched_cluster_active)) {
> + struct sched_domain *sdc = rcu_dereference(per_cpu(sd_cluster, target));
> + if (sdc) {
> + for_each_cpu_wrap(cpu, sched_domain_span(sdc), target + 1) {
> + if (!cpumask_test_cpu(cpu, cpus))
> + continue;
> +
> + if (has_idle_core) {
> + i = select_idle_core(p, cpu, cpus, &idle_cpu);
> + if ((unsigned int)i < nr_cpumask_bits)
> + return i;
> + } else {
> + if (--nr <= 0)
> + return -1;
> + idle_cpu = __select_idle_cpu(cpu, p);
> + if ((unsigned int)idle_cpu < nr_cpumask_bits)
> + break;
> + }
> + }
> + cpumask_andnot(cpus, cpus, sched_domain_span(sdc));
> + }
> + }
> +
> for_each_cpu_wrap(cpu, cpus, target + 1) {
> if (has_idle_core) {
> i = select_idle_core(p, cpu, cpus, &idle_cpu);
> @@ -6444,7 +6468,7 @@ static int select_idle_cpu(struct task_s
> 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)
> @@ -6543,7 +6567,7 @@ static int select_idle_sibling(struct ta
> /*
> * 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_lowest_cache(prev, target) &&
> (available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
> asym_fits_capacity(task_util, prev))
> return prev;
> @@ -6569,7 +6593,7 @@ static int select_idle_sibling(struct ta
> p->recent_used_cpu = prev;
> if (recent_used_cpu != prev &&
> recent_used_cpu != target &&
> - cpus_share_cache(recent_used_cpu, target) &&
> + cpus_share_lowest_cache(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)) {
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1813,7 +1813,9 @@ DECLARE_PER_CPU(struct sched_domain __rc
> DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
> DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
> DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
> +
> extern struct static_key_false sched_asym_cpucapacity;
> +extern struct static_key_false sched_cluster_active;
>
> struct sched_group_capacity {
> atomic_t ref;
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -670,7 +670,9 @@ DEFINE_PER_CPU(struct sched_domain_share
> DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa);
> DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
> DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
> +
> DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);
> +DEFINE_STATIC_KEY_FALSE(sched_cluster_active);
>
> static void update_top_cache_domain(int cpu)
> {
> @@ -2268,6 +2270,7 @@ build_sched_domains(const struct cpumask
> struct rq *rq = NULL;
> int i, ret = -ENOMEM;
> bool has_asym = false;
> + bool has_cluster = false;
>
> if (WARN_ON(cpumask_empty(cpu_map)))
> goto error;
> @@ -2289,6 +2292,7 @@ build_sched_domains(const struct cpumask
> sd = build_sched_domain(tl, cpu_map, attr, sd, i);
>
> has_asym |= sd->flags & SD_ASYM_CPUCAPACITY;
> + has_cluster |= sd->flags & SD_CLUSTER;
>
> if (tl == sched_domain_topology)
> *per_cpu_ptr(d.sd, i) = sd;
> @@ -2399,6 +2403,9 @@ build_sched_domains(const struct cpumask
> if (has_asym)
> static_branch_inc_cpuslocked(&sched_asym_cpucapacity);
>
> + if (has_cluster)
> + static_branch_inc_cpuslocked(&sched_cluster_active);
> +
> if (rq && sched_debug_verbose) {
> pr_info("root domain span: %*pbl (max cpu_capacity = %lu)\n",
> cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
> @@ -2498,6 +2505,9 @@ static void detach_destroy_domains(const
> if (rcu_access_pointer(per_cpu(sd_asym_cpucapacity, cpu)))
> static_branch_dec_cpuslocked(&sched_asym_cpucapacity);
>
> + if (rcu_access_pointer(per_cpu(sd_cluster, cpu)))
> + static_branch_dec_cpuslocked(&sched_cluster_active);
> +
> rcu_read_lock();
> for_each_cpu(i, cpu_map)
> cpu_attach_domain(NULL, &def_root_domain, i);
Thanks
Barry
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