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Message-ID: <CAKfTPtCrMAft5t8BrLxgLVoaLHoAmhTp3zgeB8Cu-7+fMSd2zw@mail.gmail.com>
Date: Fri, 11 Dec 2020 16:22:38 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Mel Gorman <mgorman@...hsingularity.net>,
Valentin Schneider <valentin.schneider@....com>,
Qais Yousef <qais.yousef@....com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
Mel Gorman <mgorman@...e.de>, Jiang Biao <benbjiang@...il.com>
Subject: Re: [RFC PATCH v8] sched/fair: select idle cpu from idle cpumask for
task wakeup
On Fri, 11 Dec 2020 at 16:19, Li, Aubrey <aubrey.li@...ux.intel.com> wrote:
>
> On 2020/12/11 23:07, Vincent Guittot wrote:
> > On Thu, 10 Dec 2020 at 02:44, Aubrey Li <aubrey.li@...ux.intel.com> wrote:
> >>
> >> Add idle cpumask to track idle cpus in sched domain. Every time
> >> a CPU enters idle, the CPU is set in idle cpumask to be a wakeup
> >> target. And if the CPU is not in idle, the CPU is cleared in idle
> >> cpumask during scheduler tick to ratelimit idle cpumask update.
> >>
> >> When a task wakes up to select an idle cpu, scanning idle cpumask
> >> has lower cost than scanning all the cpus in last level cache domain,
> >> especially when the system is heavily loaded.
> >>
> >> Benchmarks including hackbench, schbench, uperf, sysbench mysql and
> >> kbuild have been tested on a x86 4 socket system with 24 cores per
> >> socket and 2 hyperthreads per core, total 192 CPUs, no regression
> >> found.
> >>
> >> v7->v8:
> >> - refine update_idle_cpumask, no functionality change
> >> - fix a suspicious RCU usage warning with CONFIG_PROVE_RCU=y
> >>
> >> v6->v7:
> >> - place the whole idle cpumask mechanism under CONFIG_SMP
> >>
> >> v5->v6:
> >> - decouple idle cpumask update from stop_tick signal, set idle CPU
> >> in idle cpumask every time the CPU enters idle
> >>
> >> v4->v5:
> >> - add update_idle_cpumask for s2idle case
> >> - keep the same ordering of tick_nohz_idle_stop_tick() and update_
> >> idle_cpumask() everywhere
> >>
> >> v3->v4:
> >> - change setting idle cpumask from every idle entry to tickless idle
> >> if cpu driver is available
> >> - move clearing idle cpumask to scheduler_tick to decouple nohz mode
> >>
> >> v2->v3:
> >> - change setting idle cpumask to every idle entry, otherwise schbench
> >> has a regression of 99th percentile latency
> >> - change clearing idle cpumask to nohz_balancer_kick(), so updating
> >> idle cpumask is ratelimited in the idle exiting path
> >> - set SCHED_IDLE cpu in idle cpumask to allow it as a wakeup target
> >>
> >> v1->v2:
> >> - idle cpumask is updated in the nohz routines, by initializing idle
> >> cpumask with sched_domain_span(sd), nohz=off case remains the original
> >> behavior
> >>
> >> Cc: Peter Zijlstra <peterz@...radead.org>
> >> Cc: Mel Gorman <mgorman@...e.de>
> >> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> >> Cc: Qais Yousef <qais.yousef@....com>
> >> Cc: Valentin Schneider <valentin.schneider@....com>
> >> Cc: Jiang Biao <benbjiang@...il.com>
> >> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> >> Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
> >
> > This version looks good to me. I don't see regressions of v5 anymore
> > and see some improvements on heavy cases
>
> v5 or v8?
the v8 looks good to me and I don't see the regressions that I have
seen with the v5 anymore
>
> >
> > Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
> >
> >> ---
> >> include/linux/sched/topology.h | 13 ++++++++++
> >> kernel/sched/core.c | 2 ++
> >> kernel/sched/fair.c | 45 +++++++++++++++++++++++++++++++++-
> >> kernel/sched/idle.c | 5 ++++
> >> kernel/sched/sched.h | 4 +++
> >> kernel/sched/topology.c | 3 ++-
> >> 6 files changed, 70 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
> >> index 820511289857..b47b85163607 100644
> >> --- a/include/linux/sched/topology.h
> >> +++ b/include/linux/sched/topology.h
> >> @@ -65,8 +65,21 @@ struct sched_domain_shared {
> >> atomic_t ref;
> >> atomic_t nr_busy_cpus;
> >> int has_idle_cores;
> >> + /*
> >> + * Span of all idle CPUs in this domain.
> >> + *
> >> + * NOTE: this field is variable length. (Allocated dynamically
> >> + * by attaching extra space to the end of the structure,
> >> + * depending on how many CPUs the kernel has booted up with)
> >> + */
> >> + unsigned long idle_cpus_span[];
> >> };
> >>
> >> +static inline struct cpumask *sds_idle_cpus(struct sched_domain_shared *sds)
> >> +{
> >> + return to_cpumask(sds->idle_cpus_span);
> >> +}
> >> +
> >> struct sched_domain {
> >> /* These fields must be setup */
> >> struct sched_domain __rcu *parent; /* top domain must be null terminated */
> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> >> index c4da7e17b906..b136e2440ea4 100644
> >> --- a/kernel/sched/core.c
> >> +++ b/kernel/sched/core.c
> >> @@ -4011,6 +4011,7 @@ void scheduler_tick(void)
> >>
> >> #ifdef CONFIG_SMP
> >> rq->idle_balance = idle_cpu(cpu);
> >> + update_idle_cpumask(cpu, rq->idle_balance);
> >> trigger_load_balance(rq);
> >> #endif
> >> }
> >> @@ -7186,6 +7187,7 @@ void __init sched_init(void)
> >> rq->idle_stamp = 0;
> >> rq->avg_idle = 2*sysctl_sched_migration_cost;
> >> rq->max_idle_balance_cost = sysctl_sched_migration_cost;
> >> + rq->last_idle_state = 1;
> >>
> >> INIT_LIST_HEAD(&rq->cfs_tasks);
> >>
> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >> index c0c4d9ad7da8..25f36ecfee54 100644
> >> --- a/kernel/sched/fair.c
> >> +++ b/kernel/sched/fair.c
> >> @@ -6146,7 +6146,12 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> >>
> >> time = cpu_clock(this);
> >>
> >> - cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
> >> + /*
> >> + * sched_domain_shared is set only at shared cache level,
> >> + * this works only because select_idle_cpu is called with
> >> + * sd_llc.
> >> + */
> >> + cpumask_and(cpus, sds_idle_cpus(sd->shared), p->cpus_ptr);
> >>
> >> for_each_cpu_wrap(cpu, cpus, target) {
> >> if (!--nr)
> >> @@ -6806,6 +6811,44 @@ balance_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> >>
> >> return newidle_balance(rq, rf) != 0;
> >> }
> >> +
> >> +/*
> >> + * Update cpu idle state and record this information
> >> + * in sd_llc_shared->idle_cpus_span.
> >> + *
> >> + * This function is called with interrupts disabled.
> >> + */
> >> +void update_idle_cpumask(int cpu, bool idle)
> >> +{
> >> + struct sched_domain *sd;
> >> + struct rq *rq = cpu_rq(cpu);
> >> + int idle_state;
> >> +
> >> + /*
> >> + * Also set SCHED_IDLE cpu in idle cpumask to
> >> + * allow SCHED_IDLE cpu as a wakeup target.
> >> + */
> >> + idle_state = idle || sched_idle_cpu(cpu);
> >> + /*
> >> + * No need to update idle cpumask if the state
> >> + * does not change.
> >> + */
> >> + if (rq->last_idle_state == idle_state)
> >> + return;
> >> + /*
> >> + * Called with irq disabled, rcu protection is not needed.
> >> + */
> >> + sd = per_cpu(sd_llc, cpu);
> >> + if (unlikely(!sd))
> >> + return;
> >> +
> >> + if (idle_state)
> >> + cpumask_set_cpu(cpu, sds_idle_cpus(sd->shared));
> >> + else
> >> + cpumask_clear_cpu(cpu, sds_idle_cpus(sd->shared));
> >> +
> >> + rq->last_idle_state = idle_state;
> >> +}
> >> #endif /* CONFIG_SMP */
> >>
> >> static unsigned long wakeup_gran(struct sched_entity *se)
> >> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> >> index f324dc36fc43..2c517d6a061a 100644
> >> --- a/kernel/sched/idle.c
> >> +++ b/kernel/sched/idle.c
> >> @@ -257,6 +257,11 @@ static void do_idle(void)
> >> cpuhp_report_idle_dead();
> >> arch_cpu_idle_dead();
> >> }
> >> + /*
> >> + * The CPU is about to go idle, set it in idle cpumask
> >> + * to be a wake up target.
> >> + */
> >> + update_idle_cpumask(cpu, true);
> >>
> >> arch_cpu_idle_enter();
> >>
> >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> >> index 8d1ca65db3b0..4041d5a10de5 100644
> >> --- a/kernel/sched/sched.h
> >> +++ b/kernel/sched/sched.h
> >> @@ -976,6 +976,7 @@ struct rq {
> >>
> >> unsigned char nohz_idle_balance;
> >> unsigned char idle_balance;
> >> + unsigned char last_idle_state;
> >>
> >> unsigned long misfit_task_load;
> >>
> >> @@ -1516,6 +1517,8 @@ static inline unsigned int group_first_cpu(struct sched_group *group)
> >>
> >> extern int group_balance_cpu(struct sched_group *sg);
> >>
> >> +void update_idle_cpumask(int cpu, bool idle);
> >> +
> >> #if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_SYSCTL)
> >> void register_sched_domain_sysctl(void);
> >> void dirty_sched_domain_sysctl(int cpu);
> >> @@ -1536,6 +1539,7 @@ extern void flush_smp_call_function_from_idle(void);
> >>
> >> #else /* !CONFIG_SMP: */
> >> static inline void flush_smp_call_function_from_idle(void) { }
> >> +static inline void update_idle_cpumask(int cpu, bool idle) { }
> >> #endif
> >>
> >> #include "stats.h"
> >> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> >> index 1bd7e3af904f..541bd3a7de4d 100644
> >> --- a/kernel/sched/topology.c
> >> +++ b/kernel/sched/topology.c
> >> @@ -1407,6 +1407,7 @@ sd_init(struct sched_domain_topology_level *tl,
> >> sd->shared = *per_cpu_ptr(sdd->sds, sd_id);
> >> atomic_inc(&sd->shared->ref);
> >> atomic_set(&sd->shared->nr_busy_cpus, sd_weight);
> >> + cpumask_copy(sds_idle_cpus(sd->shared), sched_domain_span(sd));
> >> }
> >>
> >> sd->private = sdd;
> >> @@ -1769,7 +1770,7 @@ static int __sdt_alloc(const struct cpumask *cpu_map)
> >>
> >> *per_cpu_ptr(sdd->sd, j) = sd;
> >>
> >> - sds = kzalloc_node(sizeof(struct sched_domain_shared),
> >> + sds = kzalloc_node(sizeof(struct sched_domain_shared) + cpumask_size(),
> >> GFP_KERNEL, cpu_to_node(j));
> >> if (!sds)
> >> return -ENOMEM;
> >> --
> >> 2.25.1
> >>
>
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