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Date: Mon, 5 Feb 2024 14:09:14 -0800
From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: alexs@kernel.org
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>,
	linux-kernel@vger.kernel.org, sshegde@linux.ibm.com
Subject: Re: [PATCH v3 3/4] sched/fair: packing func
 sched_use_asym_prio()/sched_asym_prefer()
Message-ID: <20240205220914.GA17602@ranerica-svr.sc.intel.com>
References: <20240201115447.522627-1-alexs@kernel.org>
 <20240201115447.522627-3-alexs@kernel.org>
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On Thu, Feb 01, 2024 at 07:54:46PM +0800, alexs@kernel.org wrote:
> From: Alex Shi <alexs@kernel.org>

subject:

sched/fair: packing func sched_use_asym_prio()/sched_asym_prefer()

Do not use gerund mood in the subject. Better to say:
sched/fair: Rework sched_use_asym_prio() and sched_asym_prefer()
> 
> Consolidate the functions sched_use_asym_prio() and sched_asym_prefer()
> into one. and rename sched_asym() as sched_group_asym().
> This makes the code easier to read. No functional changes.

Maybe giving more reasons?

sched_use_asym_prio() 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
of a scheduling group. Rename it as sched_group_asym().

> 
> Signed-off-by: Alex Shi <alexs@kernel.org>
> To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> To: Valentin Schneider <vschneid@redhat.com>
> To: Vincent Guittot <vincent.guittot@linaro.org>
> To: Peter Zijlstra <peterz@infradead.org>
> To: Ingo Molnar <mingo@redhat.com>
> ---
>  kernel/sched/fair.c | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8d70417f5125..44fd5e2ca642 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9747,8 +9747,15 @@ 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)
> +{
> +	/* Check if asym balance applicable, then check priorities.*/

Perhaps the comment can be made more descriptive:
	/*
	 * 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
> @@ -9768,22 +9775,18 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
>   * 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;
> -	}
>  
> -	return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);

After applying this patch there is a blank line between the comment and the
return statement. Can you remove it?

> +	if ((group->flags & SD_SHARE_CPUCAPACITY) &&
> +	    (sgs->group_weight - sgs->idle_cpus != 1))
> +		return false;
> +
> +	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 */
> @@ -9939,7 +9942,7 @@ 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;
>  	}
>  
> @@ -11038,8 +11041,7 @@ 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;
>  
> @@ -11909,8 +11911,7 @@ 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
>