How to increase maximum user cpu usage allowed on a multi core system?

[Heinz Diehl]

On 17.03.2015, stan wrote: 

> Lucky you!

Lucky? The machine was fully unusable.

> Are you using F21?  Which kernel?

Yes, this machine is on F21.

[htd at chiara ~]$ uname -a
Linux chiara.fritha.org 3.19.2-rc1-bfq #1 SMP PREEMPT Mon Mar 16 16:16:07 CET 2015 x86_64 x86_64 x86_64 GNU/Linux

It's a custom build kernel with two minor patches and the BFQ scheduler.

> So, are you using rpmbuild with the src.rpm package, or compiling
> directly from the source tree?

Directly from source.

> What happens if you use -j 4?  I would think you should get somewhere
> between 3 and 4 cores.

This is the top output when compiling a kernel with -j8 (4 cores/8 threads):

top - 18:47:16 up  9:07,  4 users,  load average: 1.77, 0.39, 0.13
Tasks: 263 total,  10 running, 253 sleeping,   0 stopped,   0 zombie
%Cpu0  : 92.3 us,  5.7 sy,  0.0 ni,  0.0 id,  0.0 wa,  1.7 hi,  0.3 si,  0.0 st
%Cpu1  : 92.7 us,  5.6 sy,  0.0 ni,  0.0 id,  0.0 wa,  1.3 hi,  0.3 si,  0.0 st
%Cpu2  : 92.3 us,  6.4 sy,  0.0 ni,  0.0 id,  0.0 wa,  1.3 hi,  0.0 si,  0.0 st
%Cpu3  : 93.3 us,  5.4 sy,  0.0 ni,  0.0 id,  0.0 wa,  1.0 hi,  0.3 si,  0.0 st
%Cpu4  : 92.3 us,  6.4 sy,  0.0 ni,  0.0 id,  0.0 wa,  1.0 hi,  0.3 si,  0.0 st
%Cpu5  : 93.0 us,  5.7 sy,  0.0 ni,  0.0 id,  0.0 wa,  1.3 hi,  0.0 si,  0.0 st
%Cpu6  : 92.7 us,  5.6 sy,  0.0 ni,  0.0 id,  0.0 wa,  1.3 hi,  0.3 si,  0.0 st
%Cpu7  : 92.3 us,  6.0 sy,  0.0 ni,  0.0 id,  0.0 wa,  1.3 hi,  0.3 si,  0.0 st
KiB Mem : 16342864 total, 12336128 free,   818288 used,  3188448 buff/cache
KiB Swap: 16777212 total, 16777212 free,        0 used. 15174260 avail Mem 

19343 root       6   0  207228  81548  16184 R  24.3  0.5   0:00.73 cc1                                                                                                                       
19359 root       6   0  196268  71812  16320 R  21.6  0.4   0:00.65 cc1                                                                                                                       
19391 root       7   0  180292  55032  16188 R  13.0  0.3   0:00.39 cc1                                                                                                                       
19423 root       7   0  171012  40864  10800 R   6.3  0.3   0:00.19 cc1                                                                                                                       
19431 root       7   0  166552  37340  10888 R   5.6  0.2   0:00.17 cc1                                                                                                                       
19447 root       6   0  155452  25596  10788 R   2.3  0.2   0:00.07 cc1                                                                                                                       
19455 root       7   0  153500  24540  10648 R   2.3  0.2   0:00.07 cc1                                                                                                                       
19463 root       7   0  150112  19440  10500 R   1.3  0.1   0:00.04 cc1

> When I tried -j, I saw all the jobs queue, but only one core was used.

Can you reproduce this behaviour with a bog standard 3.19.x?