Re: [PATCH v2] ACPI: Replace msleep() with usleep_range() in acpi_os_sleep().

[Arjan van de Ven <arjan@linux.intel.com>]

On 11/20/2024 10:03 AM, Rafael J. Wysocki wrote:
> On Tue, Nov 19, 2024 at 4:08 PM Arjan van de Ven <arjan@linux.intel.com> wrote:
>>
>> On 11/19/2024 5:42 AM, Rafael J. Wysocki wrote:
>>> On Mon, Nov 18, 2024 at 3:35 PM Arjan van de Ven <arjan@linux.intel.com> wrote:
>>>>
>>>>> And the argument seems to be that it is better to always use more
>>>>> resources in a given path (ACPI sleep in this particular case) than to
>>>>> be somewhat inaccurate which is visible in some cases.
>>>>>
>>>>> This would mean that hrtimers should always be used everywhere, but they aren't.
>>>>
>>>> more or less rule of thumb is that regular timers are optimized for not firing case
>>>> (e.g. timeouts that get deleted when the actual event happens) while hrtimers
>>>> are optimized for the case where the timer is expected to fire.
>>>
>>> I've heard that, which makes me wonder why msleep() is still there.
>>>
>>> One thing that's rarely mentioned is that programming a timer in HW
>>> actually takes time, so if it is done too often, it hurts performance
>>> through latency (even if this is the TSC deadline timer).
>>
>> yup and this is why you want to group events together "somewhat", and which is why
>> we have slack, to allow that to happen
> 
> So what do you think would be the minimum slack to use in this case?
> 
> 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.