Review Request: 8004352: build-infra: Limit JOBS on large machines

[Erik Joelsson]

On 2013-02-15 18:12, Mike Duigou wrote:
> A couple of comments;
>
> - Can you reverse steps #2 and #3? Having the hard cap last makes more sense.
I agree and will do.
> - In JDK-8007327 I requested some memory size definitions such as MEMORY_SIZE_NORMAL_HEAP for sizing of JVM heaps. The explicit "1000" should probably be replaced with the MEMORY_SIZE_NORMAL_HEAP constant. Elsewhere the value is "1100".
>
I can't find any other reference to this constant, but I can certainly 
change it to 1100. I just wanted something lower than 1024 since the 
reported amount of memory in a machine is usually somewhat lower than 
the exact multiple of 2 and the division is rounded down.
> - The CONCURRENT_BUILD_JOBS is no longer JOBS * 2. Do we think that's right?
I think it's correct that you can squeeze out a bit more performance 
from the hotspot (or jdk native) build by using cores * 2 as number of 
jobs, but any value higher than cores will affect the third bullet point 
below (don't interfere with my browser experience while I'm building). I 
also found it weird to have a different setting for hotspot and the jdk 
native build and thought this a good opportunity to unify the settings.

The problem is that if someone increases JOBS to cores * 2 for maximum 
speed, there will most likely be problems in the java source generation 
in the jdk, which is more memory intensive. My assumption is that the 
speed loss from cores * 2 to cores * 1 is small enough to not matter much.

We could fix this, but I'm not sure it's worth the effort. The user just 
wants to say something like, "go full speed while I make coffee", "leave 
some room so my terminal doesn't lock up" or "I'm running 4 builds in 
parallel, tune it down please". This could be expressed as a percentage, 
with a suitable default. For each part of the build, where we make a 
submake call, we can add a call to calculate a suitable value for the -j 
flag. Input is a factor indicating memory to cpu requirements, the 
factor from the user (set at configure or at make invocation), the 
number of cpus (from configure) and the amount of memory (from configure).

/Erik
> Mike
>
> On Feb 15 2013, at 04:06 , Erik Joelsson wrote:
>
>> The current default for number of parallel build jobs is just equal to the number of cores in the system. While this works well on many machines, there have been several reports of this not working. I have been trying to come up with a better scheme for the default and the following is something that I think will do. It has been active in the build-infra forest for a while now.
>>
>> The complaints that were raised were usually concerning one of the following:
>>
>> * A big machine with very many cpus didn't scale well when using all of them, so there is no point in trying to, it just made the build less stable. Suggestion, introduce a hard cap.
>> * A machine with lots of cpus but not as much memory would run out of memory. Suggestion, limit number of jobs on memory as well as cpus.
>> * The build eats up all my resources, leaving my browser unusable. Suggestion, don't use everything unless asked for.
>>
>> So this is what I ended up with:
>> 1. Take the min of num_cores and memory_size/1000
>> 2. Cap at 16
>> 3. If more than 4 cores, shave it to 90% rounded down to leave some room.
>>
>> The user can still override this in two ways. Either by using any of the configure arguments:
>>
>>   --with-num-cores        number of cores in the build system, e.g.
>>                           --with-num-cores=8 [probed]
>>   --with-memory-size      memory (in MB) available in the build system, e.g.
>>                           --with-memory-size=1024 [probed]
>>   --with-jobs             number of parallel jobs to let make run [calculated
>>                           based on cores and memory]
>>
>> Or by setting JOBS=<number>  on the make command line.
>>
>> Also not that this change will set the CONCURRENT_BUILD_JOBS for hotspot to the value of JOBS so that it too will be overridden by the above.
>>
>> http://cr.openjdk.java.net/~erikj/8004352/webrev.root.01/
>>
>> /Erik