RFR: JDK-8138864 Build with nice to lower UI impact

[Magnus Ihse Bursie]

On 2015-10-05 13:28, Stanislav Baiduzhyi wrote:
> On 05/10/15 11:21, Magnus Ihse Bursie wrote:
>> Since building the OpenJDK is a heavy operation, the build system tries
>> to make use as of much of the system resources as possible and 
>> reasonable.
>>
>> However, on most machines except extremely high-end, this means that few
>> resources are available for other processes. On a developer machine,
>> building means that other work can get laggy and have poor response 
>> times.
>>
>> There is a simple remedy for this! Using "nice" to lower the priority
>> for the build process, so the build will wait for normal UI processes. A
>> single "nice" when handling the parallel targets in Init.gmk is 
>> sufficient.
>>
>> A potential problem could be if this affects performance on dedicated
>> build servers. I have checked this on Oracle's internal build system,
>> and there were no measurable regressions. This also stands to reason,
>> since if there would be, the build server would be running other
>> processes competing with the build. On a correctly setup build server,
>> this should not be the case. And if such processes existed, it would be
>> bad anyway.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8138864
>> WebRev:
>> http://cr.openjdk.java.net/~ihse/JDK-8138864-make-nice-priority/webrev.01 
>>
>
> But why not just add some recommendations to the readme file to 
> building section? For example, on my system I have crazy powerful CPU 
> but HDD is the bottleneck, so for me the most useful command will be:
>
> ionice -n 7 -c 3 make images
>
> And to achieve absolutely no impact on the system:
>
> nice -n 19 chrt -b 0 ionice -n 7 -c 3 make images
>

Trimming the build system for optimal performance on a specific piece of 
hardware is a story on it's own. We want to provide suitable defaults 
that are likely to at least work OK and at least not work really bad on 
all systems and for all users.

I think it would be nice to have some collected documentation on how to 
tweak build performance, and if we had, your advice would fit right in 
there. Unfortunately, the documentation is as always underprioritized. :-(

/Magnus