Messages in this thread | | | Subject | Re: Is: Default governor regardless of cpuidle driver Was: [PATCH v2] cpuidle-haltpoll: vcpu hotplug support | From | Daniel Lezcano <> | Date | Thu, 29 Aug 2019 19:42:05 +0200 |
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On 29/08/2019 19:16, Joao Martins wrote: > On 8/29/19 4:10 PM, Joao Martins wrote: >> When cpus != maxcpus cpuidle-haltpoll will fail to register all vcpus >> past the online ones and thus fail to register the idle driver. >> This is because cpuidle_add_sysfs() will return with -ENODEV as a >> consequence from get_cpu_device() return no device for a non-existing >> CPU. >> >> Instead switch to cpuidle_register_driver() and manually register each >> of the present cpus through cpuhp_setup_state() callback and future >> ones that get onlined. This mimmics similar logic that intel_idle does. >> >> Fixes: fa86ee90eb11 ("add cpuidle-haltpoll driver") >> Signed-off-by: Joao Martins <joao.m.martins@oracle.com> >> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> >> --- > > While testing the above, I found out another issue on the haltpoll series. > But I am not sure what is best suited to cpuidle framework, hence requesting > some advise if below is a reasonable solution or something else is preferred. > > Essentially after haltpoll governor got introduced and regardless of the cpuidle > driver the default governor is gonna be haltpoll for a guest (given haltpoll > governor doesn't get registered for baremetal). Right now, for a KVM guest, the > idle governors have these ratings: > > * ladder -> 10 > * teo -> 19 > * menu -> 20 > * haltpoll -> 21 > * ladder + nohz=off -> 25 > > When a guest is booted with MWAIT and intel_idle is probed and sucessfully > registered, we will end up with a haltpoll governor being used as opposed to > 'menu' (which used to be the default case). This would prevent IIUC that other > C-states get used other than poll_state (state 0) and state 1. > > Given that haltpoll governor is largely only useful with a cpuidle-haltpoll > it doesn't look reasonable to be the default? What about using haltpoll governor > as default when haltpoll idle driver registers or modload.
Are the guest and host kernel the same? IOW compiled with the same kernel config?
> My idea to achieve the above would be to decrease the rating to 9 (before the > lowest rated governor) and retain old defaults before haltpoll. Then we would > allow a cpuidle driver to define a preferred governor to switch on idle driver > registration. Naturally all of would be ignored if overidden by > cpuidle.governor=. >
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