linux-kernel - Re: [PATCH 2/3] core vruntime comparison

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Date:   Tue, 6 Aug 2019 16:17:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Aaron Lu <aaron.lu@...ux.alibaba.com>
Cc:     Aubrey Li <aubrey.intel@...il.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Tim Chen <tim.c.chen@...ux.intel.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: [PATCH 2/3] core vruntime comparison

On Thu, Jul 25, 2019 at 10:32:49PM +0800, Aaron Lu wrote:
> +bool cfs_prio_less(struct task_struct *a, struct task_struct *b)
> +{
> +	struct sched_entity *sea = &a->se;
> +	struct sched_entity *seb = &b->se;
> +	bool samecpu = task_cpu(a) == task_cpu(b);
> +	struct task_struct *p;
> +	s64 delta;
> +
> +	if (samecpu) {
> +		/* vruntime is per cfs_rq */
> +		while (!is_same_group(sea, seb)) {
> +			int sea_depth = sea->depth;
> +			int seb_depth = seb->depth;
> +
> +			if (sea_depth >= seb_depth)
> +				sea = parent_entity(sea);
> +			if (sea_depth <= seb_depth)
> +				seb = parent_entity(seb);
> +		}
> +
> +		delta = (s64)(sea->vruntime - seb->vruntime);
> +		goto out;
> +	}
> +
> +	/* crosscpu: compare root level se's vruntime to decide priority */
> +	while (sea->parent)
> +		sea = sea->parent;
> +	while (seb->parent)
> +		seb = seb->parent;
> +	delta = (s64)(sea->vruntime - seb->vruntime);
> +
> +out:
> +	p = delta > 0 ? b : a;
> +	trace_printk("picked %s/%d %s: %Ld %Ld %Ld\n", p->comm, p->pid,
> +			samecpu ? "samecpu" : "crosscpu",
> +			sea->vruntime, seb->vruntime, delta);
> +
> +	return delta > 0;
>  }

Heh.. I suppose the good news is that Rik is trying very hard to kill
the nested runqueues, which would make this _much_ easier again.