linux-kernel - Re: [RFC PATCH 1/3] sched: Introduce new interface for scheduler soft affinity

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Date:   Tue, 2 Jul 2019 18:23:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     subhra mazumdar <subhra.mazumdar@...cle.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
        prakash.sangappa@...cle.com, dhaval.giani@...cle.com,
        daniel.lezcano@...aro.org, vincent.guittot@...aro.org,
        viresh.kumar@...aro.org, tim.c.chen@...ux.intel.com,
        mgorman@...hsingularity.net
Subject: Re: [RFC PATCH 1/3] sched: Introduce new interface for scheduler
 soft affinity

On Wed, Jun 26, 2019 at 03:47:16PM -0700, subhra mazumdar wrote:
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 1183741..b863fa8 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -652,6 +652,8 @@ struct task_struct {
>  	unsigned int			policy;
>  	int				nr_cpus_allowed;
>  	cpumask_t			cpus_allowed;

You're patching dead code, that no longer exists.

> +	cpumask_t			cpus_preferred;
> +	bool				affinity_unequal;

Urgh, no. cpumask_t is an abomination and having one of them is already
unfortunate, having two is really not sane, esp. since for 99% of the
tasks they'll be exactly the same.

Why not add cpus_ptr_soft or something like that, and have it point at
cpus_mask by default, and when it needs to not be the same, allocate a
cpumask for it. That also gets rid of that unequal thing.