linux-kernel - Re: [RFC PATCH 07/13] sched: Add core wide task selection and scheduling.

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Date:   Thu, 21 May 2020 19:16:31 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     vpillai <vpillai@...italocean.com>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>, mingo@...nel.org,
        tglx@...utronix.de, pjt@...gle.com, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, fweisbec@...il.com,
        keescook@...omium.org, kerrnel@...gle.com,
        Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>, aubrey.li@...ux.intel.com,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Aaron Lu <aaron.lu@...ux.alibaba.com>
Subject: Re: [RFC PATCH 07/13] sched: Add core wide task selection and
 scheduling.

On Thu, May 21, 2020 at 07:14:26PM -0400, Joel Fernandes wrote:
> On Wed, Mar 04, 2020 at 04:59:57PM +0000, vpillai wrote:
[snip]
> > +	/*
> > +	 * If class_pick is idle or matches cookie, return early.
> > +	 */
> > +	if (cookie_equals(class_pick, cookie))
> > +		return class_pick;
> > +
> > +	cookie_pick = sched_core_find(rq, cookie);
> > +
> > +	/*
> > +	 * If class > max && class > cookie, it is the highest priority task on
> > +	 * the core (so far) and it must be selected, otherwise we must go with
> > +	 * the cookie pick in order to satisfy the constraint.
> > +	 */
> > +	if (prio_less(cookie_pick, class_pick) &&
> > +	    (!max || prio_less(max, class_pick)))
> > +		return class_pick;
> > +
> > +	return cookie_pick;
> > +}
> 
> I've been hating on this pick_task() routine for a while now :-). If we add
> the task to the tag tree as Peter suggested at OSPM for that other issue
> Vineeth found, it seems it could be simpler.

Sorry, I meant adding of a 0-tagged (no cookie) task to the tag tree.

thanks,

 - Joel