RFR: 8201788: Number of make jobs wrong for bootcycle-images target

[Erik Joelsson]

Hello,

On 2018-04-19 08:58, Severin Gehwolf wrote:
> Hi Erik,
>
> Thanks for the review!
>
> On Thu, 2018-04-19 at 08:25 -0700, Erik Joelsson wrote:
>> Hello Severin,
>>
>> The suggested patch is not a good idea because by setting -j on the make
>> command line in a sub make disables the job server. The job server is
>> what makes it possible to do recursive make with a fixed global number
>> of "jobs". If you do as you suggest, you essentially double the total
>> number of available "jobs". The original make retains its number and the
>> submake get a full other set of the same number of "jobs".
> I'm confused. Isn't this what the status quo is? With the difference
> that it's currently setting JOBS="", thus allowing sub-make to add any
> number of jobs. It'll result in sub-make calling "make -j" where '-j'
> won't get an argument. If that's the case it's disabling the job server
> currently too, no? Then again, why would we see build failures? I must
> be missing something.
Ah, correct, the current code is also disabling the job server, that is 
the core of the issue. :) I'm sorry I wasn't clear on that, it was just 
so obvious in my world. Any -j flag in a sub make disables the job 
server connection between the calling make an the sub make. Setting it 
to -j without argument is going to wreck a lot more havoc than setting 
it to something like close to "number-of-cpus", which your first 
suggestion does. The former more or less creates a fork bomb, while the 
latter only over allocates by a factor 2 at the worst.
>> My suggestion was to explicitly turn off the setting of JOBS based on a
>> special variable flag, just for bootcycle builds. Magnus didn't like
>> that because introducing a lot of special flags everywhere will
>> eventually lead to very convoluted code. He instead suggested that the
>> bootcycle call should continue to set JOBS to empty, then the code in
>> Init.gmk which sets the -j flag should be changed to:
>>
>> $(if $(JOBS), -j=$(JOBS))
>>
>> So that we only set -j if JOBS have a value. My only objection to that
>> was that we then no longer support the case of letting make run with any
>> number of jobs. I do agree that removing that option isn't a big deal.
>> You can always work around it by setting JOBS to a very large number
>> (like 1000, which is way more than any possible concurrency currently
>> possible in the build anyway).
>>
>> So to summarize, I think the correct solution to the bug is the snippet
>> above.
> Alright. How does this webrev look to you?
> http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8201788/webrev.01/
Yes, this looks good. Consider it reviewed.

/Erik
> Thanks,
> Severin
>
>> /Erik
>>
>>
>> On 2018-04-19 07:46, Severin Gehwolf wrote:
>>> Hi,
>>>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8201788
>>>
>>> I'd like to get a fix in for an old discussion which already happened a
>>> while ago:
>>> http://mail.openjdk.java.net/pipermail/build-dev/2017-April/018929.html
>>>
>>> The issue is that for bootcycle-images target a recursive call to make
>>> is being called with 'JOBS=""' which results in a call to "make -j".
>>> Thus, make is free to use as many jobs as it would like. This may cause
>>> for the occasional build failure. It has for us in the past.
>>>
>>> In this old thread above a patch like this was discouraged, unless I
>>> misunderstood something.
>>>
>>> diff --git a/make/Main.gmk b/make/Main.gmk
>>> --- a/make/Main.gmk
>>> +++ b/make/Main.gmk
>>> @@ -321,7 +321,7 @@
>>>            ifneq ($(COMPILE_TYPE), cross)
>>>             $(call LogWarn, Boot cycle build step 2: Building a new JDK image using previously built image)
>>>             +$(MAKE) $(MAKE_ARGS) -f $(TOPDIR)/make/Init.gmk PARALLEL_TARGETS=$(BOOTCYCLE_TARGET) \
>>> -             JOBS= SPEC=$(dir $(SPEC))bootcycle-spec.gmk main
>>> +             JOBS=$(JOBS) SPEC=$(dir $(SPEC))bootcycle-spec.gmk main
>>>            else
>>>             $(call LogWarn, Boot cycle build disabled when cross compiling)
>>>            endif
>>>
>>> It's my understanding that such a fix would pass down the relevant JOBS
>>> setting to sub-make and, thus, producing the desired 'make -j <JOBS>'
>>> call? What am I missing? If somebody wants to shoot themselves in the
>>> foot by doing:
>>>
>>> configure ...
>>> make JOBS=
>>>
>>> That should be fine as it would just result in "make -j" calls without
>>> arguments. The common case where the JOBS setting comes from configure
>>> would be fixed, though. bootcycle-images target would result in "make
>>> -j <num-cores>".
>>>
>>> Thoughts? Suggestions?
>>>
>>> Thanks,
>>> Severin
>>