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Re: RFC [testsuite] Obey --load-average

On 08/06/2017 05:05 PM, Daniel Santos wrote:
> On 08/03/2017 11:45 AM, Jeff Law wrote:
>> On 08/02/2017 11:34 PM, Daniel Santos wrote:
>> So does this perform better than make -j X -l X?  I use that with good
>> success.
>> jeff
> Sorry for my slow response!
> For a short answer, if you have 8 CPU cores and you run make -j8 -l8
> check then everything is fine until cron needs to do something that eats
> 4 CPUs and you end up with a load average of 12.  This is because the
> make jobs of the test harness are very long running and make's only
> control lever for regulating load is to not start new jobs until the
> load falls.  So if all jobs are already launched, make has no way of
> reducing the load until all tests on that test set have completed.
That's not something I typically see in practice.  On my local machine
I'm not usually awake when cron jobs are running, so if the load spikes
due to over-subscription I don't much care :-)

The case that is of most interest to me is the effects on shared servers
and folks that don't consistently use -l to throttle their jobs.  Your
patches would probably help in that situation by throttling parallelism
independent of the -l flags.

The second place where your stuff probably helps in a meaningful way is
over-subscription due to parallelism within the gomp testsuite.

I'll leave it to Mike who does most of the review work for the testing
infrastructure these days.  I won't objects on any philosophical grounds :-)


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