Hello Aleksey,
We very deliberately added the automatic niceness for a better general
user experience. This was back when build-infra was new and we started
pushing the parallelism of the build to where the UIs of our development
systems became annoyingly slow and sluggish when building. So, I would
be very against removing it completely, but I certainly think it should
be possible to opt out. We should never force such a behavior on an
unwilling user. My only defense is that this was done so early so we
probably didn't think about it. If you would like to provide a patch
adding a configure arg for disabling it, it would certainly be welcome.
/Erik
On 2018-10-18 01:08, Aleksey Shipilev wrote:
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
