linux-kernel - Re: [RFC PATCH v3 00/16] Core scheduling v3

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Date:   Thu, 8 Aug 2019 14:47:31 +0800
From:   Aaron Lu <aaron.lu@...ux.alibaba.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v3 00/16] Core scheduling v3

On Tue, Aug 06, 2019 at 02:19:57PM -0700, Tim Chen wrote:
> +void account_core_idletime(struct task_struct *p, u64 exec)
> +{
> +	const struct cpumask *smt_mask;
> +	struct rq *rq;
> +	bool force_idle, refill;
> +	int i, cpu;
> +
> +	rq = task_rq(p);
> +	if (!sched_core_enabled(rq) || !p->core_cookie)
> +		return;

I don't see why return here for untagged task. Untagged task can also
preempt tagged task and force a CPU thread enter idle state.
Untagged is just another tag to me, unless we want to allow untagged
task to coschedule with a tagged task.

> +	cpu = task_cpu(p);
> +	force_idle = false;
> +	refill = true;
> +	smt_mask = cpu_smt_mask(cpu);
> +
> +	for_each_cpu(i, smt_mask) {
> +		if (cpu == i)
> +			continue;
> +
> +		if (cpu_rq(i)->core_forceidle)
> +			force_idle = true;
> +
> +		/* Only refill if everyone has run out of allowance */
> +		if (cpu_rq(i)->core_idle_allowance > 0)
> +			refill = false;
> +	}
> +
> +	if (force_idle)
> +		rq->core_idle_allowance -= (s64) exec;
> +
> +	if (rq->core_idle_allowance < 0 && refill) {
> +		for_each_cpu(i, smt_mask) {
> +			cpu_rq(i)->core_idle_allowance += (s64) SCHED_IDLE_ALLOWANCE;
> +		}
> +	}
> +}