linux-kernel - Re: [PATCH] cros_ec_spi: Even though we're RT priority, don't bump cpu freq

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Message-ID: <20200612140031.4rrnbmdcb3hv755h@e107158-lin.cambridge.arm.com>
Date:   Fri, 12 Jun 2020 15:00:31 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Doug Anderson <dianders@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        hsinyi@...omium.org, Joel Fernandes <joelaf@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Gwendal Grignou <gwendal@...omium.org>,
        ctheegal@...eaurora.org, Guenter Roeck <groeck@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cros_ec_spi: Even though we're RT priority, don't bump
 cpu freq

On 06/12/20 14:47, Quentin Perret wrote:

[...]

> > > > somehow measure whether or not the task is making its deadlines and
> > > > boost the CPU frequency up if deadlines are not being met.  I'm sure
> > > > there are fancier ways.
> > 
> > You need to use SCHED_DEADLINE then :)
> 
> Well, not quite :-)
> 
> The frequency selection for DL is purely based on the userspace-provided
> parameters, from which we derive the bandwidth request. But we don't do
> things like 'raise the frequency if the actual runtime gets close to the
> WCET', or anything of the sort. All of that would have to be implemented
> in userspace ATM.

Hmm okay. I am not a deadline expert so sorry if I was misleading. But it's the
only scheduling class that has the concept of deadline.

Cheers

--
Qais Yousef