Re: [PATCH V3 0/4] cpufreq: cppc: Add support for frequency invariance
From: Viresh Kumar <viresh.kumar@linaro.org>
Date: 2021-06-29 05:20:40
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On 28-06-21, 12:54, Ionela Voinescu wrote:
If you happen to have the data around, I would like to know more about your observations on ThunderX2. I tried ThunderX2 as well, with the following observations: Booting with userspace governor and all CPUs online, the CPPC frequency scale factor was all over the place (even much larger than 1024). My initial assumptions: - Counters do not behave properly in light of SMT - Firmware does not do a good job to keep the reference and core counters monotonic: save and restore at core off. So I offlined all CPUs with the exception of 0, 32, 64, 96 - threads of a single core (part of policy0). With this all works very well:
Interesting.
root@target:/sys/devices/system/cpu/cpufreq/policy0# echo 1056000 > scaling_setspeed root@target:/sys/devices/system/cpu/cpufreq/policy0# [ 1863.095370] CPU96: cppc scale: 697. [ 1863.175370] CPU0: cppc scale: 492. [ 1863.215367] CPU64: cppc scale: 492. [ 1863.235366] CPU96: cppc scale: 492. [ 1863.485368] CPU32: cppc scale: 492. root@target:/sys/devices/system/cpu/cpufreq/policy0# echo 1936000 > scaling_setspeed root@target:/sys/devices/system/cpu/cpufreq/policy0# [ 1891.395363] CPU96: cppc scale: 558. [ 1891.415362] CPU0: cppc scale: 595. [ 1891.435362] CPU32: cppc scale: 615. [ 1891.465363] CPU96: cppc scale: 635. [ 1891.495361] CPU0: cppc scale: 673. [ 1891.515360] CPU32: cppc scale: 703. [ 1891.545360] CPU96: cppc scale: 738. [ 1891.575360] CPU0: cppc scale: 779. [ 1891.605360] CPU96: cppc scale: 829. [ 1891.635360] CPU0: cppc scale: 879. root@target:/sys/devices/system/cpu/cpufreq/policy0# root@target:/sys/devices/system/cpu/cpufreq/policy0# echo 2200000 > scaling_setspeed root@target:/sys/devices/system/cpu/cpufreq/policy0# [ 1896.585363] CPU32: cppc scale: 1004. [ 1896.675359] CPU64: cppc scale: 973. [ 1896.715359] CPU0: cppc scale: 1024. I'm doing a rate limited printk only for increase/decrease values over 64 in the scale factor value. This showed me that SMT is handled properly. Then, as soon as I start onlining CPUs 1, 33, 65, 97, the scale factor stops being even close to correct, for example: [238394.770328] CPU96: cppc scale: 22328. [238395.628846] CPU96: cppc scale: 245. [238516.087115] CPU96: cppc scale: 930. [238523.385009] CPU96: cppc scale: 245. [238538.767473] CPU96: cppc scale: 936. [238538.867546] CPU96: cppc scale: 245. [238599.367932] CPU97: cppc scale: 2728. [238599.859865] CPU97: cppc scale: 452. [238647.786284] CPU96: cppc scale: 1438. [238669.604684] CPU96: cppc scale: 27306. [238676.805049] CPU96: cppc scale: 245. [238737.642902] CPU97: cppc scale: 2035. [238737.664995] CPU97: cppc scale: 452. [238788.066193] CPU96: cppc scale: 2749. [238788.110192] CPU96: cppc scale: 245. [238817.231659] CPU96: cppc scale: 2698. [238818.083687] CPU96: cppc scale: 245. [238845.466850] CPU97: cppc scale: 2990. [238847.477805] CPU97: cppc scale: 452. [238936.984107] CPU97: cppc scale: 1590. [238937.029079] CPU97: cppc scale: 452. [238979.052464] CPU97: cppc scale: 911. [238980.900668] CPU97: cppc scale: 452. [239149.587889] CPU96: cppc scale: 803. [239151.085516] CPU96: cppc scale: 245. [239303.871373] CPU64: cppc scale: 956. [239303.906837] CPU64: cppc scale: 245. [239308.666786] CPU96: cppc scale: 821. [239319.440634] CPU96: cppc scale: 245. [239389.978395] CPU97: cppc scale: 4229. [239391.969562] CPU97: cppc scale: 452. [239415.894738] CPU96: cppc scale: 630. [239417.875326] CPU96: cppc scale: 245. The counter values shown by feedback_ctrs do not seem monotonic even when only core 0 threads are online. ref:2812420736 del:166051103 ref:3683620736 del:641578595 ref:1049653440 del:1548202980 ref:2099053440 del:2120997459 ref:3185853440 del:2714205997 ref:712486144 del:3708490753 ref:3658438336 del:3401357212 ref:1570998080 del:2279728438 For now I was just wondering if you have seen the same and whether you have an opinion on this.
I think we also saw numbers like this, which didn't explain a lot on ThunderX2. We thought they may be due to rounding issues, but the offlining stuff adds an interesting factor to that. -- viresh