On 05/12/23 16:35, Ionela Voinescu wrote:
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Hi Sumit,
On Friday 01 Dec 2023 at 18:32:10 (+0530), Sumit Gupta wrote:
Hi Ionela,
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1756,7 +1756,8 @@ static unsigned int cpufreq_verify_current_freq(struct cpufreq_policy *policy, b
{
unsigned int new_freq;
- new_freq = cpufreq_driver->get(policy->cpu);
+ new_freq = arch_freq_get_on_cpu(policy->cpu);
+ new_freq = new_freq ?: cpufreq_driver->get(policy->cpu);
Given that arch_freq_get_on_cpu() is an average frequency, it does not
seem right to me to trigger the sync & update process of
cpufreq_verify_current_freq() based on it.
cpufreq_verify_current_freq() will at least modify the internal state of
the policy and send PRE and POST notifications, if not do a full frequency
update, based on this average frequency, which is likely different from
the current frequency, even beyond the 1MHz threshold.
While I believe it's okay to return this average frequency in
cpuinfo_cur_freq, I don't think it should be used as an indication of
an accurate current frequency, which is what
cpufreq_verify_current_freq() expects.
Sumit, can you give more details on the issue at [1] and why this change
fixes it?
[1] https://lore.kernel.org/lkml/6a5710f6-bfbb-5dfd-11cd-0cd02220cee7@xxxxxxxxxx/
Thank you,
Ionela.
cpufreq_verify_current_freq() also updates 'policy->cur' in POST
notification if the frequency from hardware has more delta (out of sync).
As the value from 'cpufreq_driver->get()' is not reliable due to [1],
calling the 'get' hook can update the 'policy->cur' with a wrong value when
governor starts in cpufreq_start_governor().
And if the frequency is never changed after the governor starts during
boot e.g. when performance governor is set as default, then
'scaling_cur_freq' always returns wrong value.
Instead, the arch_freq_get_on_cpu() API updates 'policy->cur' with a more
stable freq value.
[1] https://lore.kernel.org/lkml/20230418113459.12860-7-sumitg@xxxxxxxxxx/
Got it, many thanks!
As the code is right now in v2, arch_freq_get_on_cpu() is called on
show_scaling_cur_freq(), so the problem you describe would not show up.
policy->cur would still be incorrect, but 'scaling_cur_freq' would
return the value from arch_freq_get_on_cpu().
Would it be enough if arch_freq_get_on_cpu() gets also called from
show_cpuinfo_cur_freq() instead of cpufreq_verify_current_freq()?
Thanks,
Ionela.
Yes.
I am not sure if making both the nodes 'scaling_cur_freq' and
'cpuinfo_cur_freq' same is fine?
Best Regards,
Sumit Gupta
