On Fri, Dec 13, 2019 at 8:14 AM Laura Abbott <labbott(a)redhat.com> wrote:
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.