On Monday 28 Jun 2021 at 14:14:14 (+0200), Vincent Guittot wrote: > On Mon, 28 Jun 2021 at 13:54, Ionela Voinescu <ionela.voinescu@xxxxxxx> wrote: > > > > Hi guys, > > > > On Monday 21 Jun 2021 at 14:49:33 (+0530), Viresh Kumar wrote: > > > Hello, > > > > > > Changes since V2: > > > > > > - We don't need start_cpu() and stop_cpu() callbacks anymore, we can make it > > > work using policy ->init() and exit() alone. > > > > > > - Two new cleanup patches 1/4 and 2/4. > > > > > > - Improved commit log of 3/4. > > > > > > - Dropped WARN_ON(local_freq_scale > 1024), since this can occur on counter's > > > overlap (seen with Vincent's setup). > > > > > > > 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: > > > > 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. > > > > With the counter being 32bits and the freq scaling being update at > tick, you can easily get a overflow on it in idle system. I can easily > imagine that when you unplug CPUs there is enough activity on the CPU > to update it regularly whereas with all CPUs, the idle time is longer > that the counter overflow > Thanks! Yes, given the high wraparound time I thought they were 64 bit. All variables in software are 64 bit, but looking at bit width in the _CPC entries, the platform counters are 32 bit counters. > There are 32bits and the overflow need to be handled by cppc_cpufreq > driver I'm wondering if this would be best handled in the function that reads the counters or in the cppc_cpufreq driver that uses them. Probably the latter, as you say, as the read function should only return the raw values, but it does complicate things. Thanks, Ionela. > > 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. > > > > > This is tested on my Hikey platform (without the actual read/write to > > > performance counters), with this script for over an hour: > > > > > > while true; do > > > for i in `seq 1 7`; > > > do > > > echo 0 > /sys/devices/system/cpu/cpu$i/online; > > > done; > > > > > > for i in `seq 1 7`; > > > do > > > echo 1 > /sys/devices/system/cpu/cpu$i/online; > > > done; > > > done > > > > > > > > > The same is done by Vincent on ThunderX2 and no issues were seen. > > > > Hotplug worked fine for me as well on both platforms I tested (Juno R2 > > and ThunderX2). > > > > Thanks, > > Ionela.
