On Mon, Oct 8, 2018 at 5:11 PM Waldemar Rymarkiewicz
<[email protected]> wrote:
>
> From: Waldemar Rymarkiewicz <[email protected]>
>
> The governor updates dbs_info->requested_freq only after increasing or
> decreasing frequency. There is, however, an use case when this is not
> sufficient.
>
> Imagine, external module constraining cpufreq policy in a way that policy->max
Is the "external module" here a utility or a demon running in user space?
> = policy->min = max_available_freq (eg. 1Ghz). CPUfreq will set freq to
> max_freq and conservative gov will not try downscale/upscale due to the
> limits. It will just exit instead
>
> if (requested_freq > policy->max || requested_freq < policy->min)
> //max=min=1Ghz -> requested_freq=cur=1Ghz
> requested_freq = policy->cur;
> [...]
> if (requested_freq == policy->max)
> goto out;
>
> In a result, dbs_info->requested_freq is not updated with newly calculated
> requested_freq=1Ghz. Next, execution of update routine will use again
> previously stored requested_freq (in my case it was min_available_freq)
>
> [...]
> unsigned int requested_freq = dbs_info->requested_freq;
> [....]
>
> Now, when external module returns to previous policy limits that is
> policy->min = min_available_freq and policy->max = max_available_freq,
> conservative governor is not able to decrease frequency because stored
> requested_freq is still or rather already set to min_available_freq so
> the check (for decreasing)
>
> [...]
> if (load < cs_tuners->down_threshold) {
> [....]
> if (requested_freq == policy->min)
> goto out;
> [...]
>
> returns from routine before it does any freq change. To fix that just update
> dbs_info->requested_freq every time we go out from the update routine.
>
> Signed-off-by: Waldemar Rymarkiewicz <[email protected]>
> ---
> drivers/cpufreq/cpufreq_conservative.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq_conservative.c
> b/drivers/cpufreq/cpufreq_conservative.c
> index f20f20a..7f90f6e 100644
> --- a/drivers/cpufreq/cpufreq_conservative.c
> +++ b/drivers/cpufreq/cpufreq_conservative.c
> @@ -113,7 +113,6 @@ static unsigned int cs_dbs_update(struct cpufreq_policy
> *policy)
> requested_freq = policy->max;
>
> __cpufreq_driver_target(policy, requested_freq,
> CPUFREQ_RELATION_H);
> - dbs_info->requested_freq = requested_freq;
> goto out;
> }
>
> @@ -136,10 +135,10 @@ static unsigned int cs_dbs_update(struct cpufreq_policy
> *policy)
> requested_freq = policy->min;
>
> __cpufreq_driver_target(policy, requested_freq,
> CPUFREQ_RELATION_L);
> - dbs_info->requested_freq = requested_freq;
> }
>
> out:
> + dbs_info->requested_freq = requested_freq;
This will have a side effect when requested_freq is updated before the
thresholds checks due to the policy_dbs->idle_periods < UINT_MAX
check.
Shouldn't that be avoided?
> return dbs_data->sampling_rate;
> }
