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Subject[PATCH] cpufreq: conservative: Fix requested_freq handling
Date
From: Waldemar Rymarkiewicz <waldemarx.rymarkiewicz@intel.com>

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
= 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 <waldemarx.rymarkiewicz@intel.com>
---
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;
return dbs_data->sampling_rate;
}

--
2.10.1
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