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SubjectRe: [PATCH v2.2 4/4] cpufreq: schedutil: Always call driver if CPUFREQ_NEED_UPDATE_LIMITS is set
On 29-10-20, 12:12, 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 let the driver
> callback run if the CPUFREQ_NEED_UPDATE_LIMITS cpufreq driver flag
> is set regardless of whether or not the new frequency to set is
> equal to the previous one.
>
> Fixes: f6ebbcf08f37 ("cpufreq: intel_pstate: Implement passive mode with HWP enabled")
> Reported-by: Zhang Rui <rui.zhang@intel.com>
> Tested-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>
> ---
>
> v2.1 -> v2.2:
> * Instead of updating need_freq_update if CPUFREQ_NEED_UPDATE_LIMITS is set
> in get_next_freq() and checking it again in sugov_update_next_freq(),
> check CPUFREQ_NEED_UPDATE_LIMITS directly in sugov_update_next_freq().
> * Update the subject.
>
> v2 -> v2.1:
> * Fix typo in the subject.
> * Make get_next_freq() and sugov_update_next_freq() ignore the
> sg_policy->next_freq == next_freq case when CPUFREQ_NEED_UPDATE_LIMITS
> is set for the driver.
> * Add Tested-by from Rui (this version lets the driver callback run more
> often than the v2, so the behavior in the Rui's case doesn't change).
>
> ---
> kernel/sched/cpufreq_schedutil.c | 6 ++++--
> 1 file changed, 4 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
> @@ -102,7 +102,8 @@ 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 &&
> + !cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS))
> return false;

Since sg_policy->next_freq is used elsewhere as well, this is the best
we can do here.

> sg_policy->next_freq = next_freq;
> @@ -161,7 +162,8 @@ static unsigned int get_next_freq(struct
>
> freq = map_util_freq(util, freq, max);
>
> - if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
> + if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update &&
> + !cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS))
> return sg_policy->next_freq;
>
> sg_policy->need_freq_update = false;

But I was wondering if instead of this we just do this here:

if (!cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS))
sg_policy->cached_raw_freq = freq;

And so the above check will always fail.

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

--
viresh

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