On 24-06-20, 23:46, Wei Wang wrote:
> To avoid reducing the frequency of a CPU prematurely, we skip reducing
> the frequency if the CPU had been busy recently.
>
> This should not be done when the limits of the policy are changed, for
> example due to thermal throttling. We should always get the frequency
> within the new limits as soon as possible.
>
> There was a fix in
> commit 600f5badb78c ("cpufreq: schedutil: Don't skip freq update when
> limits change") upstream which introduced another flag. However, the
> fix didn't address the case when next_freq is the same as previously
> voted, which is then checked in sugov_update_next_freq. As a result, the
> frequency would be stuck at low until the high demanding workload quits.
>
> test trace:
> kworker/u19:0-1872 ( 1872) [002] .... 347.878871: cpu_frequency_limits:
> min=600000 max=2348000 cpu_id=6
> dhry64-11525 (11525) [007] d.h2 347.880012:
> sugov_should_update_freq: thermal limit on policy6
> dhry64-11525 (11525) [007] d.h2 347.880012: sugov_deferred_update:
> policy6 skipped update
> dhry64-11525 (11525) [007] d.h2 347.884040: sugov_deferred_update:
> policy6 skipped update
I am not sure these are helpful in the logs as the code which
generated them isn't there in the kernel.
> ...
>
> This patch fixes this by skipping the check and forcing an update in
> this case. The second flag was kept as the limits_change flag could be
> updated in thermal kworker from another CPU.
I am sorry but I am not fully sure of what the problem is. Can you
describe that by giving an example with some random frequency, and
tell the expected and actual behavior ?
> Fixes: ecd288429126 ("cpufreq: schedutil: Don't set next_freq to UINT_MAX")
> Signed-off-by: Wei Wang <w...@google.com>
> ---
> kernel/sched/cpufreq_schedutil.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c
> b/kernel/sched/cpufreq_schedutil.c
> index 7fbaee24c824..dc2cd768022e 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -102,11 +102,12 @@ static bool sugov_should_update_freq(struct
> sugov_policy *sg_policy, u64 time)
> 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->need_freq_update && sg_policy->next_freq == next_freq)
AFAIU, if the next freq is same as currently programmed one, there is
no need to force update it.
> return false;
>
> sg_policy->next_freq = next_freq;
> sg_policy->last_freq_update_time = time;
> + sg_policy->need_freq_update = false;
>
> return true;
> }
> @@ -178,7 +179,6 @@ static unsigned int get_next_freq(struct sugov_policy
> *sg_policy,
> if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
> return sg_policy->next_freq;
>
> - sg_policy->need_freq_update = false;
> sg_policy->cached_raw_freq = freq;
> return cpufreq_driver_resolve_freq(policy, freq);
> }
> --
> 2.27.0.212.ge8ba1cc988-goog
--
viresh
