--- 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?
That would happen anyway if arch_freq_get_on_cpu() is called from
cpufreq_verify_current_freq().
Yes, that will happen in both the cases.
In principle, according to [1], it would be correct to use it for
'cpuinfo_cur_freq' and not 'scaling_cur_freq'. But the call from
show_scaling_cur_freq() is already there before these patches,
introduced a long time ago for x86.
The topic was discussed at [2] and the agreement so far was that it
would be best to keep the behaviour the same for both x86 and arm.
Looking at the previous discussion in [2], seems to be fine.
Best Regards,
Sumit Gupta
I don't like going against the user-guide, but these patches don't
actually go against the user-guide. The old call to
arch_freq_get_on_cpu() from show_scaling_cur_freq() goes against it.
But I agree that's something necessary to keep, as legacy for x86.
Additionally, you also mentioned that you'd prefer to have a more
accurate frequency returned for 'scaling_cur_freq'.
[1] https://www.kernel.org/doc/Documentation/cpu-freq/user-guide.txt
[2] https://lore.kernel.org/lkml/20230609043922.eyyqutbwlofqaddz@vireshk-i7/
Thanks,
Ionela.
Best Regards,
Sumit Gupta
