Does running a parallel "make -jN check" work safely?

[Kaveh R. Ghazi]

 > From: Jim Wilson <wilson@specifixinc.com>
 > 
 > Kaveh R. Ghazi wrote:
 > > I'm wondering whether running "make -jN check" is safe.  I'm
 > 
 > I have problems with the java testsuite when I use make -jN.  Some of 
 > the java tests are self-timing.  They time a loop, use that timing info 
 > to set a timer, and then do something that might hang.  See for instance 
 > libjava/testsuite/libjava.lang/Thread_Interrupt.java.  These tests work 
 > fine normally, but are unreliable with make -jN.  I suspect that the 
 > changing load average disrupts the timing of them.  I avoid parallel 
 > make checks because of this problem.  I am talking about using N > 
 > number of processors here.  Maybe they work OK if N <= number of processors.
 > 
 > If your target is a simulator, and you have a broken simulator that 
 > requires the dejagnu testglue.o file, then running tests in parallel may 
 > fail because of conflicts with the testglue.o file.  This one might have 
 > been fixed though; I am not sure.

Thanks for the info.  I get random libjava Thread_* failures
regardless. :-/ I don't use a sim so can't say much about that.

The thing I was worried about was if I run multilib passes (e.g. -m32
vs -m64 on sparc-solaris) whether it would run those in parallel too
and clobber the identically named executable for testcase.c with -m32
and testcase.c with -m64.

When Brad said he used parallel check regularly, I decided to give it
a try comparing serial vs -j10 (on a 32-cpu box).  It seems to work
fine when the results were diff'ed.  Turns out that multiple passes in
$RUNTESTFLAGS are executed serially.  So that wasn't an issue.

Therefore, the maximum parallelization you'll get for "make -jN check"
is one thread for each of the gcc, g++, g77, objc, libstdc++-v3,
libjava and libffi testsuites.  (More if you bootstrap with Ada and/or
treelang, but I generally don't.)  So in my case, you'll achieve
maximum benefit at -j7.  That's a vast improvement, BTW and allows me
to run with extra passes more often.  I've made -jN a standard part of
my scripts that test GCC now.

		Thanks,
		--Kaveh
--
Kaveh R. Ghazi			ghazi@caip.rutgers.edu