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Date: Tue, 13 Feb 2024 17:51:49 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: alexs@...nel.org
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>,
"open list:SCHEDULER" <linux-kernel@...r.kernel.org>,
Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH v5 3/5] sched/fair: Rework sched_use_asym_prio() and sched_asym_prefer()
On Sat, 10 Feb 2024 at 12:36, <alexs@...nel.org> wrote:
>
> From: Alex Shi <alexs@...nel.org>
>
> sched_use_asym_prio() and sched_asym_prefer() are used together in various
> places. Consolidate them into a single function sched_asym().
>
> The existing sched_group_asym() is only used when collecting statistics
nit: The existing sched_asym()
> of a scheduling group. Rename it as sched_group_asym(), and remove the
> obsolete function description.
>
> This makes the code easier to read. No functional changes.
>
> Tested-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> Signed-off-by: Alex Shi <alexs@...nel.org>
> Cc: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Reviewed-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
> kernel/sched/fair.c | 45 ++++++++++++++++++++-------------------------
> 1 file changed, 20 insertions(+), 25 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 607dc310b355..426eda9eda57 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9746,8 +9746,18 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
> return sd->flags & SD_SHARE_CPUCAPACITY || is_core_idle(cpu);
> }
>
> +static inline bool sched_asym(struct sched_domain *sd, int dst_cpu, int src_cpu)
> +{
> + /*
> + * First check if @dst_cpu can do asym_packing load balance. Only do it
> + * if it has higher priority than @src_cpu.
> + */
> + return sched_use_asym_prio(sd, dst_cpu) &&
> + sched_asym_prefer(dst_cpu, src_cpu);
> +}
> +
> /**
> - * sched_asym - Check if the destination CPU can do asym_packing load balance
> + * sched_group_asym - Check if the destination CPU can do asym_packing balance
> * @env: The load balancing environment
> * @sgs: Load-balancing statistics of the candidate busiest group
> * @group: The candidate busiest group
> @@ -9755,34 +9765,21 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
> * @env::dst_cpu can do asym_packing if it has higher priority than the
> * preferred CPU of @group.
> *
> - * SMT is a special case. If we are balancing load between cores, @env::dst_cpu
> - * can do asym_packing balance only if all its SMT siblings are idle. Also, it
> - * can only do it if @group is an SMT group and has exactly on busy CPU. Larger
> - * imbalances in the number of CPUS are dealt with in find_busiest_group().
> - *
> - * If we are balancing load within an SMT core, or at PKG domain level, always
> - * proceed.
> - *
> * Return: true if @env::dst_cpu can do with asym_packing load balance. False
> * otherwise.
> */
> static inline bool
> -sched_asym(struct lb_env *env, struct sg_lb_stats *sgs, struct sched_group *group)
> +sched_group_asym(struct lb_env *env, struct sg_lb_stats *sgs, struct sched_group *group)
> {
> - /* Ensure that the whole local core is idle, if applicable. */
> - if (!sched_use_asym_prio(env->sd, env->dst_cpu))
> - return false;
> -
> /*
> - * CPU priorities does not make sense for SMT cores with more than one
> + * CPU priorities do not make sense for SMT cores with more than one
> * busy sibling.
> */
> - if (group->flags & SD_SHARE_CPUCAPACITY) {
> - if (sgs->group_weight - sgs->idle_cpus != 1)
> - return false;
> - }
> + if ((group->flags & SD_SHARE_CPUCAPACITY) &&
> + (sgs->group_weight - sgs->idle_cpus != 1))
> + return false;
>
> - return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
> + return sched_asym(env->sd, env->dst_cpu, group->asym_prefer_cpu);
> }
>
> /* One group has more than one SMT CPU while the other group does not */
> @@ -9938,7 +9935,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
> /* Check if dst CPU is idle and preferred to this group */
> if (!local_group && env->sd->flags & SD_ASYM_PACKING &&
> env->idle != CPU_NOT_IDLE && sgs->sum_h_nr_running &&
> - sched_asym(env, sgs, group)) {
> + sched_group_asym(env, sgs, group)) {
> sgs->group_asym_packing = 1;
> }
>
> @@ -11037,8 +11034,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
> * SMT cores with more than one busy sibling.
> */
> if ((env->sd->flags & SD_ASYM_PACKING) &&
> - sched_use_asym_prio(env->sd, i) &&
> - sched_asym_prefer(i, env->dst_cpu) &&
> + sched_asym(env->sd, i, env->dst_cpu) &&
> nr_running == 1)
> continue;
>
> @@ -11908,8 +11904,7 @@ static void nohz_balancer_kick(struct rq *rq)
> * preferred CPU must be idle.
> */
> for_each_cpu_and(i, sched_domain_span(sd), nohz.idle_cpus_mask) {
> - if (sched_use_asym_prio(sd, i) &&
> - sched_asym_prefer(i, cpu)) {
> + if (sched_asym(sd, i, cpu)) {
> flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
> goto unlock;
> }
> --
> 2.43.0
>
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