On 12/13/19 8:49 PM, Peter Robinson wrote: >>> On 12/12/19 9:10 AM, Justin Forbes wrote: >>>> On Thu, Dec 12, 2019 at 3:48 AM Peter Robinson <pbrobinson@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxx> >>>> 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? I don't know of a reason -- pbonzini? Have any input here? P. > > P > _______________________________________________ > kernel mailing list -- kernel@xxxxxxxxxxxxxxxxxxxxxxx > To unsubscribe send an email to kernel-leave@xxxxxxxxxxxxxxxxxxxxxxx > 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@xxxxxxxxxxxxxxxxxxxxxxx > _______________________________________________ kernel mailing list -- kernel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to kernel-leave@xxxxxxxxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxxxxxxxxxx
