On Tue, Jul 17, 2018 at 09:33:53AM +0200, Rafael J. Wysocki wrote: > Hi, > > Thanks for your report! > > On Tue, Jul 17, 2018 at 8:50 AM, Andreas Herrmann <aherrm...@suse.com> wrote: > > Hello, > > > > I've recently noticed that commit 554c8aa8ecad ("sched: idle: Select > > idle state before stopping the tick") causes severe performance drop > > for systems using pcc-cpufreq driver. Depending on the number of CPUs > > the system might be almost unusable. The OS jitter for 4.17.y and > > 4.18.-rcx kernels is off the charts, you can even spot it with top > > command (issued when the system is supposedly idle), e.g. > > > > top - 14:44:24 up 2 min, 1 user, load average: 90.11, 38.20, 14.38 > > Tasks: 1199 total, 109 running, 541 sleeping, 0 stopped, 0 zombie > > %Cpu(s): 1.2 us, 58.7 sy, 0.0 ni, 39.3 id, 0.6 wa, 0.0 hi, 0.3 si, > > 0.0 st > > KiB Mem: 13137064+total, 1192168 used, 13017848+free, 2340 buffers > > KiB Swap: 2104316 total, 0 used, 2104316 free. 522296 cached Mem > > > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ > > COMMAND > > 3373 root 20 0 982024 49916 36120 R 96.691 0.038 0:19.54 > > kubelet > > 67 root 20 0 0 0 0 R 78.676 0.000 0:49.36 > > kworker/9:0 > > 25 root 20 0 0 0 0 R 78.125 0.000 0:49.67 > > kworker/2:0 > > 182 root 20 0 0 0 0 R 75.735 0.000 1:18.17 > > kworker/28:0 > > 43 root 20 0 0 0 0 R 75.000 0.000 0:11.56 > > kworker/5:0 > > 103 root 20 0 0 0 0 R 74.449 0.000 0:46.83 > > kworker/15:0 > > 334 root 20 0 0 0 0 R 72.978 0.000 1:06.88 > > kworker/53:0 > > 789 root 20 0 0 0 0 R 69.853 0.000 1:29.50 > > kworker/38:1 > > 418 root 20 0 0 0 0 R 69.301 0.000 0:41.33 > > kworker/67:0 > > 779 root 20 0 0 0 0 R 68.934 0.000 1:33.60 > > kworker/27:1 > > 773 root 20 0 0 0 0 R 68.566 0.000 1:37.91 > > kworker/22:1 > > 762 root 20 0 0 0 0 R 68.015 0.000 1:41.01 > > kworker/11:1 > > 769 root 20 0 0 0 0 R 67.647 0.000 1:37.65 > > kworker/18:1 > > 805 root 20 0 0 0 0 R 67.096 0.000 1:30.96 > > kworker/54:1 > > 840 root 20 0 0 0 0 R 66.912 0.000 1:23.82 > > kworker/89:1 > > 812 root 20 0 0 0 0 R 66.728 0.000 1:31.89 > > kworker/59:1 > > 847 root 20 0 0 0 0 R 66.360 0.000 1:28.40 > > kworker/96:1 > > 763 root 20 0 0 0 0 R 66.176 0.000 1:42.57 > > kworker/12:1 > > 772 root 20 0 0 0 0 R 66.176 0.000 1:12.58 > > kworker/21:1 > > 821 root 20 0 0 0 0 R 66.176 0.000 1:29.62 > > kworker/69:1 > > 923 root 20 0 0 0 0 R 65.809 0.000 1:44.32 > > kworker/3:18 > > 1284 root 20 0 0 0 0 R 65.809 0.000 1:23.50 > > kworker/101:2 > > 61 root 20 0 0 0 0 R 65.625 0.000 1:29.37 > > kworker/8:0 > > 3531 root 20 0 24384 3768 2356 R 65.625 0.003 0:08.91 top > > 771 root 20 0 0 0 0 R 65.074 0.000 1:37.90 > > kworker/20:1 > > 767 root 20 0 0 0 0 R 64.706 0.000 1:38.01 > > kworker/16:1 > > 764 root 20 0 0 0 0 R 64.522 0.000 1:40.28 > > kworker/13:1 > > 765 root 20 0 0 0 0 R 64.154 0.000 1:40.13 > > kworker/14:1 > > > > When I apply below patch (trying to revert essential parts of commit > > 554c8aa8ecad) behaviour seems back to normal. > > Well, that basically defeats the purpose of the change in commit > 554c8aa8ecad, so it's not what I'd like to do to fix this problem. > > Also it would be good to understand what actually happens. > > > I know that pcc-cpufreq driver is not "state-of-the-art" when it comes > > to cpufreq drivers and you better not use it. > > That's exactly right. > > > But I wonder whether commit 554c8aa8ecad ("sched: idle: Select idle state > > before > > stopping the tick") introduced bad behaviour for other cases as well. > > It has been tested quite extensively in that respect, although > admittedly not with the pcc-cpufreq driver. > > Nothing bad related to it has been has been reported so far, FWIW. > > > I'll send some performance results to illustrate the issue asap. I've > > also tried to modify pcc-cpufreq to reduce the amount of frequency > > changes triggered by this driver but this does not help for kernels > > where commit 554c8aa8ecad is applied. > > Can you replace pcc-cpufreq with a different cpufreq driver on the > affected systems? If so, do performance numbers look bad after that > too?
I have no performance numbers yet for other cpufreq drivers on this system (checking this commit). But I'll look it at next. Andreas