linux-kernel - Re: [PATCH v3 5/6] sched/fair: Consider SMT in ASYM

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Date:   Mon, 17 May 2021 17:18:29 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Len Brown <len.brown@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        Quentin Perret <qperret@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, Aubrey Li <aubrey.li@...el.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v3 5/6] sched/fair: Consider SMT in ASYM_PACKING load
 balance

On 13/05/2021 17:49, Ricardo Neri wrote:

[...]

> @@ -8447,6 +8456,89 @@ group_type group_classify(unsigned int imbalance_pct,
>  	return group_has_spare;
>  }
>  
> +/**
> + * asym_can_pull_tasks - Check whether the load balancing CPU can pull tasks
> + * @dst_cpu:	Destination CPU of the load balancing
> + * @sds:	Load-balancing data with statistics of the local group
> + * @sgs:	Load-balancing statistics of the candidate busiest group
> + * @sg:		The candidate busiet group
> + *
> + * Check the state of the SMT siblings of both @sds::local and @sg and decide
> + * if @dst_cpu can pull tasks. If @dst_cpu does not have SMT siblings, it can
> + * pull tasks if two or more of the SMT siblings of @sg are busy. If only one
> + * CPU in @sg is busy, pull tasks only if @dst_cpu has higher priority.
> + *
> + * If both @dst_cpu and @sg have SMT siblings. Even the number of idle CPUs
> + * between @sds::local and @sg. Thus, pull tasks from @sg if the difference
> + * between the number of busy CPUs is 2 or more. If the difference is of 1,
> + * only pull if @dst_cpu has higher priority. If @sg does not have SMT siblings
> + * only pull tasks if all of the SMT siblings of @dst_cpu are idle and @sg
> + * has lower priority.
> + */
> +static bool asym_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds,
> +				struct sg_lb_stats *sgs, struct sched_group *sg)
> +{
> +#ifdef CONFIG_SCHED_SMT
> +	int cpu, local_busy_cpus, sg_busy_cpus;
> +	bool local_is_smt, sg_is_smt;
> +
> +	cpu = group_first_cpu(sg);

Looks like `cpu` isn't used.

[...]