Hi, Aubrey On Fri, 11 Sep 2020 at 23:48, Aubrey Li <aubrey...@intel.com> wrote: > > Added idle cpumask to track idle cpus in sched domain. When a CPU > enters idle, its corresponding bit in the idle cpumask will be set, > and when the CPU exits idle, its bit will be cleared. > > When a task wakes up to select an idle cpu, scanning idle cpumask > has low cost than scanning all the cpus in last level cache domain, > especially when the system is heavily loaded. > > Signed-off-by: Aubrey Li <aubrey...@linux.intel.com> > --- > include/linux/sched/topology.h | 13 +++++++++++++ > kernel/sched/fair.c | 4 +++- > kernel/sched/topology.c | 2 +- > 3 files changed, 17 insertions(+), 2 deletions(-) > > diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h > index fb11091129b3..43a641d26154 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/fair.c b/kernel/sched/fair.c > index 6b3b59cc51d6..3b6f8a3589be 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6136,7 +6136,7 @@ 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); > + cpumask_and(cpus, sds_idle_cpus(sd->shared), p->cpus_ptr); Is the sds_idle_cpus() always empty if nohz=off? Do we need to initialize the idle_cpus_span with sched_domain_span(sd)?
> > for_each_cpu_wrap(cpu, cpus, target) { > if (!--nr) > @@ -10182,6 +10182,7 @@ static void set_cpu_sd_state_busy(int cpu) > sd->nohz_idle = 0; > > atomic_inc(&sd->shared->nr_busy_cpus); > + cpumask_clear_cpu(cpu, sds_idle_cpus(sd->shared)); > unlock: > rcu_read_unlock(); > } > @@ -10212,6 +10213,7 @@ static void set_cpu_sd_state_idle(int cpu) > sd->nohz_idle = 1; > > atomic_dec(&sd->shared->nr_busy_cpus); > + cpumask_set_cpu(cpu, sds_idle_cpus(sd->shared)); This only works when entering/exiting tickless mode? :) Why not update idle_cpus_span during tick_nohz_idle_enter()/exit()? Thx. Regards, Jiang > unlock: > rcu_read_unlock(); > } > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 9079d865a935..92d0aeef86bf 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -1769,7 +1769,7 @@ 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 >