Re: Abysmal scheduler performance in Linus' tree?

From: Peter Zijlstra
Date: Wed Sep 06 2017 - 04:25:27 EST

On Tue, Sep 05, 2017 at 10:13:39PM -0700, Andy Lutomirski wrote:
> I'm running e7d0c41ecc2e372a81741a30894f556afec24315 from Linus' tree
> today, and I'm seeing abysmal scheduler performance. Running make -j4
> ends up with all the tasks on CPU 3 most of the time (on my
> 4-logical-thread laptop). taskset -c 0 whatever puts whatever on CPU
> 0, but plain while true; do true; done puts the infinite loop on CPU 3
> right along with the make -j4 tasks.
>
> This is on Fedora 26, and I don't think I'm doing anything weird.
> systemd has enabled the cpu controller, but it doesn't seem to have
> configured anything or created any non-root cgroups.
>
> Just a heads up. I haven't tried to diagnose it at all.

"make O=defconfig-build -j80" results in:

%Cpu0 : 90.7 us, 9.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu1 : 88.7 us, 11.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu2 : 93.5 us, 6.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu3 : 86.8 us, 13.2 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu4 : 89.7 us, 10.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu5 : 96.3 us, 3.7 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu6 : 95.3 us, 4.7 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu7 : 94.4 us, 5.6 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu8 : 91.7 us, 8.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu9 : 94.3 us, 5.7 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu10 : 90.7 us, 9.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu11 : 96.2 us, 3.8 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu12 : 91.5 us, 8.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu13 : 90.6 us, 9.4 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu14 : 97.2 us, 2.8 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu15 : 89.7 us, 10.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu16 : 90.6 us, 9.4 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu17 : 93.4 us, 6.6 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu18 : 90.6 us, 9.4 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu19 : 92.5 us, 7.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu20 : 94.4 us, 5.6 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu21 : 90.7 us, 9.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu22 : 92.5 us, 7.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu23 : 90.7 us, 9.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu24 : 91.6 us, 8.4 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu25 : 93.5 us, 6.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu26 : 93.4 us, 5.7 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.9 si, 0.0 st
%Cpu27 : 92.5 us, 7.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu28 : 92.5 us, 7.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu29 : 88.8 us, 11.2 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu30 : 90.6 us, 9.4 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu31 : 93.5 us, 6.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu32 : 93.5 us, 6.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu33 : 93.4 us, 6.6 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu34 : 90.7 us, 9.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu35 : 93.5 us, 6.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu36 : 90.7 us, 9.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu37 : 97.2 us, 2.8 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu38 : 92.5 us, 7.5 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu39 : 92.6 us, 7.4 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st

Do you have a .config somewhere? Are you running with the systemd? Is it
creating cpu cgroups?

Any specifics on your setup?