[lkml]   [2019]   [Aug]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Is: Default governor regardless of cpuidle driver Was: [PATCH v2] cpuidle-haltpoll: vcpu hotplug support
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 <>
>> Signed-off-by: Boris Ostrovsky <>
>> ---
> 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=.

<> │ Open source software for ARM SoCs

Follow Linaro: <> Facebook |
<!/linaroorg> Twitter |
<> Blog

 \ /
  Last update: 2019-08-29 19:43    [W:0.106 / U:23.004 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site