On 2021/1/15 18:08, Mel Gorman wrote:
> From: Peter Zijlstra (Intel) <pet...@infradead.org>
>
> Instead of calculating how many (logical) CPUs to scan, compute how
> many cores to scan.
>
> This changes behaviour for anything !SMT2.
>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
> ---
> kernel/sched/core.c | 18 +++++++++++++-----
> kernel/sched/fair.c | 12 ++++++++++--
> kernel/sched/sched.h | 2 ++
> 3 files changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 15d2562118d1..ada8faac2e4d 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7444,11 +7444,19 @@ int sched_cpu_activate(unsigned int cpu)
> balance_push_set(cpu, false);
>
> #ifdef CONFIG_SCHED_SMT
> - /*
> - * When going up, increment the number of cores with SMT present.
> - */
> - if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
> - static_branch_inc_cpuslocked(&sched_smt_present);
> + do {
> + int weight = cpumask_weight(cpu_smt_mask(cpu));
> +
> + if (weight > sched_smt_weight)
> + sched_smt_weight = weight;
> +
> + /*
> + * When going up, increment the number of cores with SMT
> present.
> + */
> + if (weight == 2)
> + static_branch_inc_cpuslocked(&sched_smt_present);
> +
> + } while (0);
> #endif
> set_cpu_active(cpu, true);
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c8d8e185cf3b..0811e2fe4f19 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6010,6 +6010,8 @@ static inline int find_idlest_cpu(struct sched_domain
> *sd, struct task_struct *p
> DEFINE_STATIC_KEY_FALSE(sched_smt_present);
> EXPORT_SYMBOL_GPL(sched_smt_present);
>
> +int sched_smt_weight __read_mostly = 1;
> +
> static inline void set_idle_cores(int cpu, int val)
> {
> struct sched_domain_shared *sds;
> @@ -6124,6 +6126,8 @@ static int select_idle_smt(struct task_struct *p,
> struct sched_domain *sd, int t
>
> #else /* CONFIG_SCHED_SMT */
>
> +#define sched_smt_weight 1
> +
> static inline int select_idle_core(struct task_struct *p, struct
> sched_domain *sd, int target)
> {
> return -1;
> @@ -6136,6 +6140,8 @@ static inline int select_idle_smt(struct task_struct
> *p, struct sched_domain *sd
>
> #endif /* CONFIG_SCHED_SMT */
>
> +#define sis_min_cores 2
> +
> /*
> * 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
> @@ -6166,10 +6172,12 @@ static int select_idle_cpu(struct task_struct *p,
> struct sched_domain *sd, int t
> avg_cost = this_sd->avg_scan_cost + 1;
>
> span_avg = sd->span_weight * avg_idle;
> - if (span_avg > 4*avg_cost)
> + if (span_avg > sis_min_cores*avg_cost)
> nr = div_u64(span_avg, avg_cost);
> else
> - nr = 4;
> + nr = sis_min_cores;
> +
> + nr *= sched_smt_weight;
Is it better to put this into an inline wrapper to hide sched_smt_weight if
!CONFIG_SCHED_SMT?
Thanks,
-Aubrey
