[LLVMdev] MultiSource/Applications/lemon slow in JIT

[Evan Cheng]

On May 21, 2008, at 6:09 AM, Matthijs Kooijman wrote:

> Hi,
>
> I've been toying around with the testsuite for a bit, and after  
> recompiling
> llvm-gcc a bunch of times and fixing a nasty bashism bug, I actually  
> got it to
> run and pass most tests.
>
> When running, I noticed a very long runtime on the lemon test. At  
> first I
> suspected an infinite loop, but it turned out the test simply needed  
> around
> 1000 seconds to run. Some investigation turned out that the lemon  
> program does
> a lot of forking (it runs every input file 20 times, so that's  
> around 200
> forks). However, since the forking happens quite early in the main  
> function,
> it happens before most of the program is JITted. So, every one of  
> these forked
> process is taking a few seconds to compile the other needed  
> functions, over
> and over again.
>
> A solution for this problem seems to be to run the lemon test with the
> -no-lazy option, so things get compiled before forking. In my case,  
> this
> reduced runtime from 1000+ seconds to only 16 seconds.
>
> Intrestingly enough, I can't seem to find similar behaviour in the  
> test
> results on llvm.org/nightlytest (though I only checked two machines  
> [since the
> results take ages to load...] of which
> only one actually ran the test). Am I the only one that is  
> experiencing this?
>
> Anyhow, the below patch fixes the problem for me, good to commit?

Ouch. I didn't notice this. I don't think passing this option is the  
right fix though. Any test that forks a lot is simply not a good  
compiler benchmark. The right thing to do is to eliminate the forking.  
Is that cannot be easily done. We should remove it from our test suite.

Thanks,

Evan


>
>
> Gr.
>
> Matthijs
>
>
> Index: MultiSource/Applications/lemon/Makefile
> ===================================================================
> --- MultiSource/Applications/lemon/Makefile     (revision 51189)
> +++ MultiSource/Applications/lemon/Makefile     (working copy)
> @@ -8,5 +8,8 @@
> include $(LEVEL)/Makefile.config
>
> include ../../Makefile.multisrc
> +
> +JIT_OPTS += -no-lazy
> +
> DIFFPROG := $(PROGDIR)/DiffOutput.sh "diff "
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev