Re: [PATCH] xen/cpufreq: Reset policy after enabling/disabling turbo status

[Jane Malalane <Jane.Malalane@xxxxxxxxxx>]

On 10/11/2021 11:48, Ian Jackson wrote:

> [CAUTION - EXTERNAL EMAIL] DO NOT reply, click links, or open attachments unless you have verified the sender and know the content is safe.
>
> Jane Malalane writes ("[PATCH] xen/cpufreq: Reset policy after enabling/disabling turbo status"):
> > Before, user would change turbo status but this had no effect: boolean
> > was set but policy wasn't reevaluated.  Policy must be reevaluated so
> > that CPU frequency is chosen according to the turbo status and the
> > current governor.
> >
> > Therefore, add __cpufreq_governor() in cpufreq_update_turbo().
> ...
> > Not taking this patch means that turbo status is misleading.
> >
> > Taking this patch is low-risk as it only uses a function that already
> > exists and is already used for setting the chosen scaling governor.
> > Essentially, this change is equivalent to running 'xenpm
> > en/disable-turbo-mode' and, subsequently, running 'xenpm
> > set-scaling-governor <current governor>'.
> Thanks.  I am positively inclined.  But I have one query about this
> rationale.  Adding a new call to an existing function is OK if calling
> __cpufreq_governor is permitted here.  Are there locking or reentrancy
> hazards ?  Perhaps these issue have been considered but I would like
> to see something explicit about that.
>
> Thanks,
Hi Ian,
I think that's not a concern here because the only other
callers of __cpufreq_governor are __cpufreq_set_policy(), which is under the
same sysctl_lock, and cpufreq_del_cpu, which shouldn't be an issue because no
further action can be performed against the cpu when that function is called.
I will have to submit a v2 of this patch, so I can add
these considerations to the release rationale section?

Thanks,

Jane.

>