RE: CPU excessively long times between frequency scaling driver calls - bisected

["Doug Smythies" <dsmythies@telus.net>]

On 2022.02.24 04:08:30 Paul E. McKenney wrote:
> On Thu, Feb 24, 2022 at 04:08:30PM +0800, Feng Tang wrote:
>> On Wed, Feb 23, 2022 at 03:23:20PM +0100, Rafael J. Wysocki wrote:
>>> On Wed, Feb 23, 2022 at 1:40 AM Feng Tang <feng.tang@intel.com> wrote:
>>> 
>>> But this is not related to idle as such, but to the fact that idle
>>> sometimes stops the scheduler tick which otherwise would run the
>>> cpufreq governor callback on a regular basis.
>>> 
>>> It is stopping the tick that gets us into trouble, so I would avoid
>>> doing it if the current performance state is too aggressive.
>> 
>> I've tried to simulate Doug's environment by using his kconfig, and
>> offline my 36 CPUs Desktop to leave 12 CPUs online, and on it I can
>> still see Local timer interrupts when there is no active load, with
>> the longest interval between 2 timer interrupts is 4 seconds, while
>> idle class's task_tick_idle() will do nothing, and CFS'
>> task_tick_fair() will in turn call cfs_rq_util_change()
>
> Every four seconds?  Could you please post your .config?
>
>							Thanx, Paul

I steal the kernel config from the Ubuntu mainline PPA.
See also earlier on this thread:

https://lore.kernel.org/linux-pm/CAAYoRsXkyWf0vmEE2HvjF6pzCC4utxTF=7AFx1PJv4Evh=C+Ow@mail.gmail.com/

but relevant part copied here:

> I steal the kernel configuration file from the Ubuntu mainline PPA
> [1], what they call "lowlatency", or 1000Hz tick. I make these
> changes before compile:
>
> scripts/config --disable DEBUG_INFO
> scripts/config --disable SYSTEM_TRUSTED_KEYS
> scripts/config --disable SYSTEM_REVOCATION_KEYS
>
> I [will] also send you the config and dmesg files in an off-list email.
>
> [1] https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.17-rc3/

I put the same one I sent Feng on my web site where I was
sharing stuff with Srinivas (coded to avoid the barrage of bots):

double u double u double u dot smythies dot com/~doug/linux/s18/hwp/srinivas/long_dur/
 
... Doug