linux-kernel - Re: [PATCH v2] cpufreq/cppc: Take policy->cur into judge when set target

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Date: Wed, 29 May 2024 11:06:52 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Riwen Lu <luriwen@...mail.com>
Cc: rafael@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Riwen Lu <luriwen@...inos.cn>
Subject: Re: [PATCH v2] cpufreq/cppc: Take policy->cur into judge when set
 target

On 29-05-24, 11:22, Riwen Lu wrote:
> From: Riwen Lu <luriwen@...inos.cn>
> 
> There is a case that desired_perf is exactly the same with the old perf,
> but the actual current freq is not. Add a judgment condition to return
> only when the three values are exactly the same.
> 
> This happened in S3 while the cpufreq governor is set to powersave.
> During resume process, the CPU frequency is adjusted to the highest
> perf. For the booting CPU, there's a warning that "CPU frequency out of
> sync:", because the policy->cur is the lowest_perf while the actual
> current frequency is the highest_perf that obtained via
> cppc_cpufreq_get_rate(), then set policy->cur to highest_perf. The
> governor->limits() intent to configure the CPU frequency to lowest_perf
> and the governor->target() returned because the desired_perf is equal to
> cpu->perf_ctrls.desired_perf leaving the actual current frequency and
> policy->cur are remain the highest_perf. Add a judgement that if
> policy->cur is the same with desired_perf to decide whther to return.
> 
> Signed-off-by: Riwen Lu <luriwen@...inos.cn>
> 
> ---
> v1 -> v2:
>  - Update commit message and email.
> ---
>  drivers/cpufreq/cppc_cpufreq.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 15f1d41920a3..802f7c7c0ad8 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -296,7 +296,8 @@ static int cppc_cpufreq_set_target(struct cpufreq_policy *policy,
>  
>  	desired_perf = cppc_khz_to_perf(&cpu_data->perf_caps, target_freq);
>  	/* Return if it is exactly the same perf */
> -	if (desired_perf == cpu_data->perf_ctrls.desired_perf)
> +	if (desired_perf == cpu_data->perf_ctrls.desired_perf &&
> +	    desired_perf == policy->cur)

>From my earlier understanding, desired_perf is a derived interpretation of the
frequency and isn't an actual frequency value which can be compared with
policy->cur.

Shouldn't we compare policy->cur with target_freq instead ? If yes, than the
core must already be doing that somewhere I guess.

-- 
viresh