Re: [PATCH RFC] tick/sched: Prevent pointless NOHZ transitions

[Thomas Gleixner]

On Tue, Feb 24 2026 at 22:31, Rafael J. Wysocki wrote:
> On Tuesday, February 24, 2026 5:13:06 PM CET Thomas Gleixner wrote:
>> So either the governor/driver muck provides some sensible default
>> implementation or this has to go into into default_idle_call().
>> 
>> Oh well...
>
> It looks like the issue is cause by the tick_nohz_idle_stop_tick() called right
> before invoking default_idle_call().
>
> After the recent changes mentioned above, cpuidle_select() will never stop the
> tick when there's only one idle state in the cpuidle driver, so it would be
> consistent to make the default case behave analogously.  The default idle state
> is never a deep one AFAICS.
>
> So maybe something like the below?
>
> ---
>  kernel/sched/idle.c |    2 --
>  1 file changed, 2 deletions(-)
>
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -186,8 +186,6 @@ static void cpuidle_idle_call(void)
>  	}
>  
>  	if (cpuidle_not_available(drv, dev)) {
> -		tick_nohz_idle_stop_tick();
> -
>  		default_idle_call();
>  		goto exit_idle;
>  	}

Which prevents VMs or other systems which do not have an idle driver to
stop the tick at all. That's just obviously wrong, no?

Thanks,

        tglx