On Thu, Feb 24, 2022 at 08:29:22AM -0800, Doug Smythies wrote:
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=7AFx1PJv4...
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/
Thank you!
I don't see CONFIG_FAST_NO_HZ=y in your .config, so that is not the reason for your every-four-second timers. ;-)
(CONFIG_FAST_NO_HZ is being removed, FYI.)
Thanx, Paul