linux-kernel - Re: [PATCH 4/5] sched/isolation: Residual 1Hz scheduler tick offload

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Message-ID: <alpine.DEB.2.20.1712191026310.18737@nuc-kabylake>
Date:   Tue, 19 Dec 2017 10:38:39 -0600 (CST)
From:   Christopher Lameter <cl@...ux.com>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Wanpeng Li <kernellwp@...il.com>,
        Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 4/5] sched/isolation: Residual 1Hz scheduler tick
 offload

On Tue, 19 Dec 2017, Peter Zijlstra wrote:

> > Depends what one means by RT.
>
> Real Time computing as per the literature. Any other definition is
> wrong and confusing.

That is an understanding of language rooted in the positivism of the early
20th century which was intending to assign a single and clear meaning to
each word (Betrand Russell f.e.). Contemporarily the meaning of words are
determined by the use cases for those words in communities and in
particular by the function of these words (See Wittgenstein).

And the term RT has been heavily abused by marketing folks to mean any
number of things so people can use RT to refer to variety of things. So
please always clarify what you mean exactly.

You mean RT in CS academic literature from the 1990s I guess? Mostly
useless for real workloads...

Frederic is probably more using the misleading characterization of
"realtime" as spread by the marketing teams of leading distros that
suggests low latency and less OS noise.

But then in business in general "realtime processing" is a term used
opposed to "offline" processing. A system that reacts in real time is a
system that continually reacts against inputs without offline processing
of data. Which can be minutes.

So lets better avoid that term entirely.