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SubjectRe: [PATCH v2 4/4] cpufreq: schedutil: Always call drvier if need_freq_update is set
Spelling mistake in $subject (driver)

On 23-10-20, 17:36, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Because sugov_update_next_freq() may skip a frequency update even if
> the need_freq_update flag has been set for the policy at hand, policy
> limits updates may not take effect as expected.
>
> For example, if the intel_pstate driver operates in the passive mode
> with HWP enabled, it needs to update the HWP min and max limits when
> the policy min and max limits change, respectively, but that may not
> happen if the target frequency does not change along with the limit
> at hand. In particular, if the policy min is changed first, causing
> the target frequency to be adjusted to it, and the policy max limit
> is changed later to the same value, the HWP max limit will not be
> updated to follow it as expected, because the target frequency is
> still equal to the policy min limit and it will not change until
> that limit is updated.
>
> To address this issue, modify get_next_freq() to clear
> need_freq_update only if the CPUFREQ_NEED_UPDATE_LIMITS flag is
> not set for the cpufreq driver in use (and it should be set for all
> potentially affected drivers) and make sugov_update_next_freq()
> check need_freq_update and continue when it is set regardless of
> whether or not the new target frequency is equal to the old one.
>
> Fixes: f6ebbcf08f37 ("cpufreq: intel_pstate: Implement passive mode with HWP enabled")
> Reported-by: Zhang Rui <rui.zhang@intel.com>
> Cc: 5.9+ <stable@vger.kernel.org> # 5.9+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>
> New patch in v2.
>
> ---
> kernel/sched/cpufreq_schedutil.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> Index: linux-pm/kernel/sched/cpufreq_schedutil.c
> ===================================================================
> --- linux-pm.orig/kernel/sched/cpufreq_schedutil.c
> +++ linux-pm/kernel/sched/cpufreq_schedutil.c
> @@ -102,11 +102,12 @@ static bool sugov_should_update_freq(str
> static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
> unsigned int next_freq)
> {
> - if (sg_policy->next_freq == next_freq)
> + if (sg_policy->next_freq == next_freq && !sg_policy->need_freq_update)
> return false;
>
> sg_policy->next_freq = next_freq;
> sg_policy->last_freq_update_time = time;
> + sg_policy->need_freq_update = false;
>
> return true;
> }
> @@ -164,7 +165,10 @@ static unsigned int get_next_freq(struct
> if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
> return sg_policy->next_freq;
>
> - sg_policy->need_freq_update = false;
> + if (sg_policy->need_freq_update)
> + sg_policy->need_freq_update =
> + cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
> +

The behavior here is a bit different from what we did in cpufreq.c. In cpufreq
core we are _always_ allowing the call to reach the driver's target() routine,
but here we do it only if limits have changed. Wonder if we should have similar
behavior here as well ?

Over that the code here can be rewritten a bit like:

if (sg_policy->need_freq_update)
sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
else if (freq == sg_policy->cached_raw_freq)
return sg_policy->next_freq;

--
viresh

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