>> On 12/12/19 9:10 AM, Justin Forbes wrote:
>>> On Thu, Dec 12, 2019 at 3:48 AM Peter Robinson <pbrobinson(a)gmail.com>
wrote:
>>>>
>>>> Hey All.
>>>>
>>>> In digging through some pieces around CPU_IDLE I noticed that
>>>> NO_HZ_IDLE is explicitly disabled on x86_64 but not on all other
>>>> architectures.
>>>>
>>>> Doing a "git log --follow
>>>> configs/fedora/generic/x86/x86_64/CONFIG_NO_HZ_IDLE" it goes all
the
>>>> way back to 2016 when we changed the way the configs were handled.
>>>>
>>>> The upstream kernel's opinion [1] on it is "Most of the time you
want
>>>> to say Y here." so I'm wondering if there's a reason why
we're
>>>> difference on x86_64 or is it just lost in the winds of time?
>>>>
>>>> Peter
>>>>
>>>> PS was digging around CPU_IDLE_GOV_TEO for those curious.
>>>>
>>>> [1]
https://cateee.net/lkddb/web-lkddb/NO_HZ_IDLE.html
>>>
>>>
>>> commit 3836faf6e68495fc70316229a3540506f7ce4c98
>>> Author: Kyle McMartin <kyle(a)fedoraproject.org>
>>> Date: Wed Sep 17 13:10:12 2014 -0500
>>>
>>> re-enable RCU_FAST_NO_HZ, enable NO_HZ_FULL on x86_64
>>>
>>> - I also like to live dangerously. (Re-enable RCU_FAST_NO_HZ which
>>> has been off
>>> since April 2012. Also enable NO_HZ_FULL on x86_64.)
>>
>> Yeah I wouldn't quite say it's been "lost" but the real
question
>> is if it still makes sense. I don't have a strong opinion without
>> data. Prarit, any opinion here?
>
> Oh, I wasn't pointing out that it wasn't just lost, I was pointing out
> that NO_HZ_IDLE is not set because we run NO_HZ_FULL. We were one of
> the first distros to do so, and it has worked well for us. I have a
> fairly strong opinion about not dropping back to IDLE without good
> reason.
This wasn't a proposal to change anything here at all, sorry if that
was the way it read. I was purely wondering, while digging through
stuff around cpu idle, for the difference between arches.
With the hit around NO_HZ_IDLE vs NO_HZ_FULL I dug some more and
basically it seems the reason we don't have the later on the non
x86_64 arches is because for some reason we unset
VIRT_CPU_ACCOUNTING_GEN for all except x86_64, it looks to be
historical, all our current architectures now look to support that
option. Anyone aware of any reason we shouldn't use the
NO_HZ_FULL/VIRT_CPU_ACCOUNTING_GEN as standard across all arches?
P
_______________________________________________
kernel mailing list -- kernel(a)lists.fedoraproject.org
To unsubscribe send an email to kernel-leave(a)lists.fedoraproject.org
Fedora Code of Conduct:
https://docs.fedoraproject.org/en-US/project/code-of-conduct/
List Guidelines:
https://fedoraproject.org/wiki/Mailing_list_guidelines
List Archives:
https://lists.fedoraproject.org/archives/list/kernel@lists.fedoraproject.org