linux-kernel - Re: iowait boost is broken

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Message-ID: <YL+tDv/EL5ogf/0w@hirez.programming.kicks-ass.net>
Date:   Tue, 8 Jun 2021 19:46:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Beata Michalska <beata.michalska@....com>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Quentin Perret <qperret@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Qais Yousef <qais.yousef@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: iowait boost is broken

On Mon, Jun 07, 2021 at 08:10:32PM +0100, Beata Michalska wrote:
> So back to the expectations.
> The main problem, as I see it, is what do we actually want to achieve with
> the I/O boosting? Is it supposed to compensate the time lost while waiting
> for the I/O request to be completed or is is supposed to optimize the rate
> at which I/O requests are being made. 

The latter, you want to increase the race of submission.

> Do we want to boost I/O bound tasks by
> default, no limits applied  or should we care about balancing performance
> vs power ? And unless those expectations are clearly stated, we might not
> get too far with any changes, really.

You want to not increase power beyond what is needed to match the rate
of processing I suppose.