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[bug #49844] 'make -j' without explicit process count sometimes doesn't


From: Dima Kogan
Subject: [bug #49844] 'make -j' without explicit process count sometimes doesn't parallelize
Date: Wed, 14 Dec 2016 19:02:17 +0000 (UTC)
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:49.0) Gecko/20100101 Firefox/49.0

URL:
  <http://savannah.gnu.org/bugs/?49844>

                 Summary: 'make -j' without explicit process count sometimes
doesn't parallelize
                 Project: make
            Submitted by: dkogan
            Submitted on: Wed 14 Dec 2016 07:02:15 PM GMT
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: None
        Operating System: None
           Fixed Release: None
           Triage Status: None

    _______________________________________________________

Details:

Hi. I have this trivial Makefile:

%:
        echo Starting $@ || true
        timeout 5 bash -c 'while true; do true; done' || true
        echo Done $@ || true

It's meant to spin the cpu for 5 seconds for each target being built. I can
ask for 5 simultaneous jobs with something like 'seq 1000 | xargs -n1000 make
-j5' and this command should always redline 5 CPUs. If I give 'make -j'
instead of 'make -j5' I would expect it to redline ALL my CPUs, but I see it
not do any parallelization at all instead. If the Makefile contains normal
(not pattern) rules, then it works how I would expect.




    _______________________________________________________

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