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Message-ID: <20221002223234.GA17621@ranerica-svr.sc.intel.com>
Date: Sun, 2 Oct 2022 15:32:34 -0700
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Ricardo Neri <ricardo.neri@...el.com>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Ben Segall <bsegall@...gle.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Steven Rostedt <rostedt@...dmis.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
linux-kernel@...r.kernel.org, "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [RFC PATCH 01/23] sched/task_struct: Introduce classes of tasks
On Tue, Sep 27, 2022 at 03:01:07PM +0200, Peter Zijlstra wrote:
> On Fri, Sep 16, 2022 at 07:41:13AM -0700, Ricardo Neri wrote:
>
> > At least on Intel processors, class 0 is a valid class. The scheduler needs to
> > have a notion of unclassified tasks and decide how to handle them, IMO.
> >
> > Intel processors currently support 8-bit, unsigned classes. I doubt other
> > architectures will ever support more than 256 classes. Short can handle all the
> > possible classification values and also the unclassified case.
> >
> > On the other hand, class 0 could be the default classification unless hardware
> > classifies differently. 0 would be special and need to be documented clearly.
> > This would work for Intel processors.
>
> You can always do: class = hw_class + 1; that makes 0 'special' and the
> hardware class can be trivially reconstructed by subtracting 1.
This makes sense to me. I will implement as you suggest.
Thanks and BR,
Ricardo
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