linux-kernel - Re: [PATCH v2] sched/fair: ignore cache hotness for SMT migration

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Message-ID: <20200810061406.GA15559@linux.vnet.ibm.com>
Date:   Mon, 10 Aug 2020 11:44:06 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Josh Don <joshdon@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/fair: ignore cache hotness for SMT migration

* Josh Don <joshdon@...gle.com> [2020-08-04 12:34:13]:

> SMT siblings share caches, so cache hotness should be irrelevant for
> cross-sibling migration.
> 
> Proposed-by: Venkatesh Pallipadi <venki@...gle.com>
> Signed-off-by: Josh Don <joshdon@...gle.com>
> ---
>  kernel/sched/fair.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1a68a0536add..abdb54e2339f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7402,6 +7402,10 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
>  	if (unlikely(task_has_idle_policy(p)))
>  		return 0;
>  
> +	/* SMT siblings share cache */
> +	if (env->sd->flags & SD_SHARE_CPUCAPACITY)
> +		return 0;
> +

If this for retaining cache hotness, should we look at
SD_SHARE_PKG_RESOURCES instead of SD_SHARE_CPUCAPACITY?

>  	/*
>  	 * Buddy candidates are cache hot:
>  	 */
> -- 
> 2.28.0.163.g6104cc2f0b6-goog
> 

-- 
Thanks and Regards
Srikar Dronamraju