Build niceness

[Erik Joelsson]

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
>