parallel testsuite results differ from a single task approach

[Dennis Clarke <dclarke@blastwave.org>]

I gad received some good advice to try using gmake -j X -k check for some X > 1 when running a testsuite in order to speed the process up. So I decided to test that theory with an eye on the results. I was surprised to see that the results when running "gmake -j 8 -k check" differ from a simple "gmake -k check" in the area of go and libmudflap : 

    1 ) parallel testsuite : 

        http://gcc.gnu.org/ml/gcc-testresults/2012-12/msg01903.html

    2 ) single process testsuite : 

        http://gcc.gnu.org/ml/gcc-testresults/2012-12/msg01935.html


In parallel we see this for "go" : 

                === go tests ===


Running target unix
FAIL: go.test/test/stack.go execution,  -O2 -g 

                === go Summary ===

# of expected passes            3293
# of unexpected failures        1
# of expected failures          4
# of untested testcases         4
/home/dclarke/pgm/build/gcc-4.7.2_2.6.32-279.14.1.el6.x86_64.004/gcc/testsuite/go/../../gccgo  version 4.7.2 (Blastwave.org Inc. time_rfc-3339=2012-12-20 11:23:25+00:00) 




While the single process apporach reports : 


                === go Summary ===

# of expected passes            3294
# of expected failures          4
# of untested testcases         4
/home/dclarke/pgm/build/gcc-4.7.2_2.6.32-279.14.1.el6.x86_64.004/gcc/testsuite/go/../../gccgo  version 4.7.2 (Blastwave.org Inc. time_rfc-3339=2012-12-20 11:23:25+00:00) 


Perhaps the go test "go.test/test/stack.go" is somehow sensitive to running on a busy machine? I am only guessing. 

The "libmudflap tests" results are wildly different. 

So at first glance it appears that the testsuite will in fact product different results if one chooses to use "gmake -j X" for X>1 but I am not sure why.  Felt is was worth pointing out as maybe no one else has done the comparison.

Dennis