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

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Date: Wed, 24 Apr 2024 12:01:27 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
	daniel.lezcano@...aro.org
Subject: Re: [PATCH 4/4] sched/core: split iowait state into two states

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?