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Re: RFC [testsuite] Obey --load-average
- From: Jeff Law <law at redhat dot com>
- To: Daniel Santos <daniel dot santos at pobox dot com>, gcc <gcc at gcc dot gnu dot org>, Rainer Orth <ro at CeBiTec dot Uni-Bielefeld dot DE>, Mike Stump <mikestump at comcast dot net>
- Date: Fri, 1 Sep 2017 16:35:20 -0600
- Subject: Re: RFC [testsuite] Obey --load-average
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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
> 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 :-)