linux-kernel - Re: [PATCH] iopoll: use fsleep() instead of usleep

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Message-ID: <7875cadfb12b1d2e8def412346d61716a6a98107@intel.com>
Date: Thu, 26 Jun 2025 18:16:23 +0300
From: Jani Nikula <jani.nikula@...el.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org, Thomas
 Gleixner <tglx@...utronix.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] iopoll: use fsleep() instead of usleep_range()

On Thu, 26 Jun 2025, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> Hi Jani,
>
> Thanks for your patch!
>
> On Thu, 26 Jun 2025 at 16:51, Jani Nikula <jani.nikula@...el.com> wrote:
>> Sometimes it's necessary to poll with long sleeps, and the accuracy of
>> usleep_range() is overkill. Use the flexible sleep helper fsleep() for
>> sleeping in the read_poll_timeout() family of macros to automatically
>> choose the appropriate method of waiting.
>>
>> Functionally there are a few consequences for existing users:
>>
>> - 10 us and shorter sleeps will use usleep() instead of
>
> s/usleep/udelay/.

D'oh!

>
>>   usleep_range(). Presumably this will not be an issue.
>
> Note that udelay() does not sleep, but loops.

Quite right. IIUC this is because for short delays it's more efficient.

BR,
Jani.

>
>>
>> - When it leads to a slack of less than 25%, msleep() will be used
>>   instead of usleep_range(). Presumably this will not be an issue, given
>>   the sleeps will be longer in this case.
>>
>> - Otherwise, the usleep_range() slack gets switched from the begin of
>>   the range to the end of the range, i.e. [sleep/2+1..sleep] ->
>>   [sleep..sleep+sleep/2]. In theory, this could be an issue in some
>>   cases, but difficult to determine before this hits the real world.
>>
>> Signed-off-by: Jani Nikula <jani.nikula@...el.com>
>
>> Not really sure who to Cc, given MAINTAINERS doesn't match this. Adding
>> some past committers.
>
> Oh well ;-)
>
> Gr{oetje,eeting}s,
>
>                         Geert

-- 
Jani Nikula, Intel