linux-kernel - Re: [PATCH 4/4] sched/core: split iowait state into two states

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Date: Thu, 25 Apr 2024 16:20:29 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Jens Axboe <axboe@...nel.dk>, Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de,
 linux-pm@...r.kernel.org, daniel.lezcano@...aro.org,
 "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 4/4] sched/core: split iowait state into two states

On Wednesday, April 24, 2024 12:01:27 PM CEST Peter Zijlstra wrote:
> On Tue, Apr 16, 2024 at 06:11:21AM -0600, Jens Axboe wrote:
> > iowait is a bogus metric, but it's helpful in the sense that it allows
> > short waits to not enter sleep states that have a higher exit latency
> > than would've otherwise have been picked for iowait'ing tasks. However,
> > it's harmless in that lots of applications and monitoring assumes that
> > iowait is busy time, or otherwise use it as a health metric.
> > Particularly for async IO it's entirely nonsensical.
> 
> Let me get this straight, all of this is about working around
> cpuidle menu governor insaity?
> 
> Rafael, how far along are we with fully deprecating that thing? Yes it
> still exists, but should people really be using it still?

Well, they appear to be used to it ...