linux-kernel - Re: [PATCH v2] ACPI: Replace msleep() with usleep_range() in acpi_os

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Message-ID: <593c4be2-c21e-49fa-8bf7-a614c01c8e66@linux.intel.com>
Date: Wed, 20 Nov 2024 11:18:41 -0800
From: Arjan van de Ven <arjan@...ux.intel.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Len Brown <lenb@...nel.org>, anna-maria@...utronix.de,
 tglx@...utronix.de, peterz@...radead.org, frederic@...nel.org,
 corbet@....net, akpm@...ux-foundation.org, linux-acpi@...r.kernel.org,
 linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Len Brown <len.brown@...el.com>, Todd Brandt <todd.e.brandt@...el.com>
Subject: Re: [PATCH v2] ACPI: Replace msleep() with usleep_range() in
 acpi_os_sleep().

On 11/20/2024 10:49 AM, Rafael J. Wysocki wrote:
>>> I thought about something on the order of 199 us, but now I'm thinking
>>> that 50 us would work too.  Less than this - I'm not sure.
>>
>> 50 usec is likely more than enough in practice.
> 
> And would you use the same slack value regardless of the sleep
> duration, or make it somehow depend on the sleep duration?

I don't see why you'd make it dependent on the sleep duration
sure in theory the longer the sleep -- you could pick a fixed percentage

but you're trying to amortize a theoretical timer register write, and a
cpu wakeup. the timer write is fixed cost and not THAT expensive after
some amount of this . the C state wake up --- sure that is more variable
but that is super important for high occurance things (thousands to millions
of times per hour).
If your ACPI sleeps are high occurance on a system I suspect you have way
bigger problems than an occasional extra wakeup