linux-kernel - Re: [PATCH 5/5] spi: Reduce kthread priority

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Message-ID: <20190801123503.GC5488@sirena.org.uk>
Date:   Thu, 1 Aug 2019 13:35:03 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        mingo@...nel.org, linux-kernel@...r.kernel.org,
        Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>, linux-spi@...r.kernel.org,
        Doug Anderson <dianders@...gle.com>
Subject: Re: [PATCH 5/5] spi: Reduce kthread priority

On Thu, Aug 01, 2019 at 02:17:18PM +0200, Peter Zijlstra wrote:

> I'm thinking that isn't true 99% of the time, except of course when that
> bandsaw emergency break is attached through SPI, but in that case the
> admin can very well chrt the prio of this thread.

The SPI thread isn't usually RT, it's only made RT if something in the
system asks for it - the reason the ChromeOS people got CCed in is that
some of their embedded controllers are very fragile and need super tight
timing on some of the interactions over their control interface so
they're one of the users here.  Of course everyone is then going to
claim that their usage is the most critical usage in the system, and
they may well even be right, but I do tend to agree that just any old RT
priority is probably a sensible default since for most cases there will
be few if any other RT tasks anyway.

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