Re: regression caused by 08f511fd41c3 ("cpufreq: Reduce cpufreq_update_util() overhead a bit")

[Rafael J. Wysocki]

On Fri, Jun 17, 2016 at 4:03 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Fri, Jun 17, 2016 at 06:16:51AM -0700, Paul E. McKenney wrote:
>> > Paul, Peter, any ideas about what may be going on here?
>>
>> Looks to me like this commit moved some code from synchronize_rcu() to
>> synchronize_sched().  Assuming that this is a CONFIG_PREEMPT=y system,
>> might there have been a decrease in the wakeups from the rcu_preempt
>> kthread?
>
> The 'funny' thing is though; those synchronize thingies are only reached
> when we change cpufreq policy, so things like:
>
>   for i in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor ; do echo performance > $i ; done

Or if you change min or max for a policy and the driver is intel_pstate.

> Something which is hardly possible when idle. Weird.

Well, exactly.

Jisheng, do you use intel_pstate or acpi-cpufreq as the scaling driver?