Re: [PATCH v2 2/7] cpufreq: set invariance scale factor on transition end

Rafael J. Wysocki
2020-07-27T13:54:25Z

On Wed, Jul 22, 2020 at 11:38 AM Ionela Voinescu
<ionela.voinescu@arm.com> wrote:
>
> While the move of the invariance setter calls (arch_set_freq_scale())
> from cpufreq drivers to cpufreq core maintained the previous
> functionality for existing drivers that use target_index() and
> fast_switch() for frequency switching, it also gives the possibility
> of adding support for users of the target() callback, which is exploited
> here.
>
> To be noted that the target() callback has been flagged as deprecated
> since:
>
> commit 9c0ebcf78fde ("cpufreq: Implement light weight ->target_index() routine")
>
> It also doesn't have that many users:
>
> cpufreq-nforce2.c:371:2: .target = nforce2_target,
> cppc_cpufreq.c:416:2: .target = cppc_cpufreq_set_target,
> gx-suspmod.c:439:2: .target = cpufreq_gx_target,
> pcc-cpufreq.c:573:2: .target = pcc_cpufreq_target,
>
> Similarly to the path taken for target_index() calls in the cpufreq core
> during a frequency change, all of the drivers above will mark the end of a
> frequency change by a call to cpufreq_freq_transition_end().
>
> Therefore, cpufreq_freq_transition_end() can be used as the location for
> the arch_set_freq_scale() call to potentially inform the scheduler of the
> frequency change.
>
> This change maintains the previous functionality for the drivers that
> implement the target_index() callback, while also adding support for the
> few drivers that implement the deprecated target() callback.
>
> Two notes are worthwhile here:
> - In __target_index(), cpufreq_freq_transition_end() is called only for
> drivers that have synchronous notifications enabled. There is only one
> driver that disables them,
>
> drivers/cpufreq/powernow-k8.c:1142: .flags = CPUFREQ_ASYNC_NOTIFICATION,
>
> which is deprecated.
>
> - Despite marking a successful frequency change, many cpufreq drivers
> will populate the new policy->cur with the new requested frequency,
> although this might not be the one granted by the hardware.
>
> Therefore, the call to arch_set_freq_scale() is a "best effort" one,
> and it is up to the architecture if the new frequency is used in the
> new frequency scale factor setting or eventually used by the scheduler.
> The architecture is in a better position to decide if it has better
> methods to obtain more accurate information regarding the current
> frequency (for example the use of counters).
>
> Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> drivers/cpufreq/cpufreq.c | 15 ++++++---------
> 1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index bac4101546db..3497c1cd6818 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -448,6 +448,10 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy,
>
> cpufreq_notify_post_transition(policy, freqs, transition_failed);
>
> + arch_set_freq_scale(policy->related_cpus,
> + policy->cur,
> + policy->cpuinfo.max_freq);
> +
> policy->transition_ongoing = false;
> policy->transition_task = NULL;
>
> @@ -2159,7 +2163,7 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
> unsigned int relation)
> {
> unsigned int old_target_freq = target_freq;
> - int index, retval;
> + int index;
>
> if (cpufreq_disabled())
> return -ENODEV;
> @@ -2190,14 +2194,7 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
>
> index = cpufreq_frequency_table_target(policy, target_freq, relation);
>
> - retval = __target_index(policy, index);
> -
> - if (!retval)
> - arch_set_freq_scale(policy->related_cpus,
> - policy->freq_table[index].frequency,
> - policy->cpuinfo.max_freq);
> -
> - return retval;
> + return __target_index(policy, index);
> }
> EXPORT_SYMBOL_GPL(__cpufreq_driver_target);
>
> --

I would fold this patch into the previous one.

I don't see much reason for it to be separate and it looks like
folding it in would cause the previous patch to be simpler.