linux-kernel - Re: [PATCH] ACPI: Remove msleep() bloat from acpi_os

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Message-ID: <CAJZ5v0gmtRAQtdi6fdUQDfLv7sKyukb3aXwsdsdtZvSH6QFRnw@mail.gmail.com>
Date: Fri, 15 Nov 2024 22:45:38 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Len Brown <lenb@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>, 
	Thomas Gleixner <tglx@...utronix.de>, linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Frederic Weisbecker <frederic@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Jonathan Corbet <corbet@....net>, 
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ACPI: Remove msleep() bloat from acpi_os_sleep()

On Fri, Nov 15, 2024 at 10:20 PM Len Brown <lenb@...nel.org> wrote:
>
> Re: if short sleep then use usleep_range()
>
> I think we all agree on this.
>
> Though in the ACPI flows that brought up this topic, setting max to
> anything other than min is simply a request for bad performance.

I disagree with the "bad performance" statement.

Performance lower than the possible maximum doesn't necessarily count as "bad".

> Re: if long sleeps then use msleep()
>
> ... because a jiffy based timer effectively forces coalescing, and is
> the lowest overhead.
>
> The problem with this logic is, as you mention, coalescing is a
> function of the distribution of timer expirations over time,it is not
> a function of the duration of those timers.

I just think that high precision is not necessary for long timeouts.

I also don't think that ASL programmers expect high precision in those cases.