Build niceness

[Aleksey Shipilev]

Hi,

Is there any specific user story behind "nice"-ing the compilation jobs from within the build system?

It unfortunately clashes with priority budgeting. For example, my build server is used by me doing
adhoc builds, automatic builds and some background tasks. The automatic build user has priority 10
set in /etc/security/limits.conf. The background user has priority 20 set in limits.conf. In theory,
it sounds good: it would get all the CPU ad-hoc builds want, then give CPU to automatic build jobs,
then to background jobs.

But then the build nice-s the compilation jobs, which drops its priority down to the priority of
background jobs:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND


25966 backgro+  39  19  808872 460772   2440 R  97.0  1.4   4181:54 R


25968 backgro+  39  19  808872 460588   2340 R  97.0  1.4   4181:17 R


25965 backgro+  39  19  808872 460864   2680 R  93.4  1.4   4180:29 R


30998 buildbot  39  19 6688224 1.050g  20000 S  64.8  3.4   4:58.52 java


27518 buildbot  39  19 2915828 110884  21740 S  47.0  0.3   0:02.57 javac


26802 buildbot  39  19  290900 264792  17392 R  38.2  0.8   0:05.48 cc1plus


27486 buildbot  39  19  200296 171792  18440 R  30.6  0.5   0:01.96 cc1plus

...which wrecks up this story. Maybe the better solution in build system is to avoid nice-ing at
all, and require users who need it to invoke "nice -n ... make ..."? Or maybe at least have the knob
that disables automatic niceness?

Thanks,
-Aleksey