Hi Feng,
Thank you for your reply.
On Mon, Feb 7, 2022 at 6:39 PM Feng Tang feng.tang@intel.com wrote:
Hi Doug,
Thanks for the report.
On Tue, Feb 08, 2022 at 09:40:14AM +0800, Doug Smythies wrote:
Hi All,
Note before: I do not know If I have the e-mail address list correct, nor am I actually a member of the x86 distribution list. I am on the linux-pm email list.
When using the intel_pstate CPU frequency scaling driver with HWP disabled, active mode, powersave scaling governor, the times between calls to the driver have never exceeded 10 seconds.
Since kernel 5.16-rc4 and commit: b50db7095fe002fa3e16605546cba66bf1b68a3e " x86/tsc: Disable clocksource watchdog for TSC on qualified platorms"
There are now occasions where times between calls to the driver can be over 100's of seconds and can result in the CPU frequency being left unnecessarily high for extended periods.
From the number of clock cycles executed between these long durations one can tell that the CPU has been running code, but the driver never got called.
Attached are some graphs from some trace data acquired using intel_pstate_tracer.py where one can observe an idle system between about 42 and well over 200 seconds elapsed time, yet CPU10 never gets called, which would have resulted in reducing it's pstate request, until an elapsed time of 167.616 seconds, 126 seconds since the last call. The CPU frequency never does go to minimum.
For reference, a similar CPU frequency graph is also attached, with the commit reverted. The CPU frequency drops to minimum, over about 10 or 15 seconds.,
commit b50db7095fe0 essentially disables the clocksource watchdog, which literally doesn't have much to do with cpufreq code.
One thing I can think of is, without the patch, there is a periodic clocksource timer running every 500 ms, and it loops to run on all CPUs in turn. For your HW, it has 12 CPUs (from the graph), so each CPU will get a timer (HW timer interrupt backed) every 6 seconds. Could this affect the cpufreq governor's work flow (I just quickly read some cpufreq code, and seem there is irq_work/workqueue involved).
6 Seconds is the longest duration I have ever seen on this processor before commit b50db7095fe0.
I said "the times between calls to the driver have never exceeded 10 seconds" originally, but that involved other processors.
I also did longer, 9000 second tests:
For a reverted kernel the driver was called 131,743, and 0 times the duration was longer than 6.1 seconds.
For a non-reverted kernel the driver was called 110,241 times, and 1397 times the duration was longer than 6.1 seconds, and the maximum duration was 303.6 seconds
Can you try one test that keep all the current setting and change the irq affinity of disk/network-card to 0xfff to let interrupts from them be distributed to all CPUs?
I am willing to do the test, but I do not know how to change the irq affinity.
Thanks, Feng
Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz
Why this particular configuration, i.e. no-hwp, active, powersave? Because it is, by far, the easiest to observe what is going on.
... Doug