Re: [PATCH v4 3/3] cpufreq: CPPC: Update FIE arch_freq_scale in ticks for non-PCC regs

[Pierre Gondois <pierre.gondois@arm.com>]

Hello Jie Zhan,


On 12/3/25 04:24, Jie Zhan wrote:
> Currently, the CPPC Frequency Invariance Engine (FIE) is invoked from the
> scheduler tick but defers the update of arch_freq_scale to a separate
> thread because cppc_get_perf_ctrs() would sleep if the CPC regs are in PCC.
>
> However, this deferred update mechanism is unnecessary and introduces extra
> overhead for non-PCC register spaces (e.g. System Memory or FFH), where
> accessing the regs won't sleep and can be safely performed from the tick
> context.
>
> Furthermore, with the CPPC FIE registered, it throws repeated warnings of
> "cppc_scale_freq_workfn: failed to read perf counters" on our platform with
> the CPC regs in System Memory and a power-down idle state enabled.  That's
> because the remote CPU can be in a power-down idle state, and reading its
> perf counters returns 0.  Moving the FIE handling back to the scheduler
> tick process makes the CPU handle its own perf counters, so it won't be
> idle and the issue would be inherently solved.
>
> To address the above issues, update arch_freq_scale directly in ticks for
> non-PCC regs and keep the deferred update mechanism for PCC regs.
>
> Signed-off-by: Jie Zhan<zhanjie9@hisilicon.com>
> ---
>   drivers/cpufreq/cppc_cpufreq.c | 77 +++++++++++++++++++++++-----------
>   1 file changed, 52 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 947b4e2e1d4e..36e8a75a37f1 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
[...]
> @@ -236,10 +265,8 @@ static void __init cppc_freq_invariance_init(void)
>   
>   static void cppc_freq_invariance_exit(void)
>   {
> -	if (fie_disabled)
> -		return;
> -
> -	kthread_destroy_worker(kworker_fie);
> +	if (kworker_fie)
> +		kthread_destroy_worker(kworker_fie);

Shouldn't we have:
   kworker_fie = NULL;
here aswell ?

>   }
>   
>   #else


Otherwise, for the 3 patches:

Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>