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

Severin Gehwolf sgehwolf at redhat.com
Thu Apr 19 18:08:03 UTC 2018


Hi Erik,

On Thu, 2018-04-19 at 09:03 -0700, Erik Joelsson wrote:
> 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.

OK. That does make it sound like that "disabling the job server" and
creating more jobs are independent problems. I somehow thought in my
naive world that disabling the job server puts an end to the fork-bomb
;-)

Thanks for the clarification.

> > > 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.

Great, thanks for the review! I'm currently running this through jdk-
submit. Hopefully I'll get some response this time :)

Cheers,
Severin

> /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
> 
> 


More information about the build-dev mailing list