On Mon, November 2, 2009 9:09 am, Simon Marlow wrote:
On 31/10/2009 18:27, Henry DeYoung wrote:
We've decided to use oprofile to sample cache misses recorded by the performance counters. To get reasonable information out of oprofile, I'd like to compile the nofib benchmarks via C with export of debugging symbols.
As a first step toward this, I've changed the NoFibHcOpts variable in nofib/mk/boilerplate.mk to be:
NoFibHcOpts = -O -fvia-C -pgmc gcc -optc-g
That won't work, I'm afraid. The Evil Mangler script that post-processes the .s file output by gcc does not understand the debug annotations added by gcc's -g flag.
The best you can do with oprofile is get assembly-level profiling. It's not too bad actually; I've used it in the past myself, although oprofile itself I found to be a bit flaky - for some reason it seems to stop counting randomly on my laptop.
You might have better luck using the new performance counter support ("performance events") in Linux 2.6.31. I've not been able to test it yet myself because apparently it doesn't support the CPU in my laptop, but I plan to find another machine to try it on soon.
So now I'm using NoFibHcOpts = -O -keep-s-files -opta-g which seems to work fine. You mentioned that assembly-level profiling is the best you can do with oprofile (in particular). Is there another profiler that would allow source-level (in Haskell or the generated C code) profiling, or is this as good as it gets for any profiler since GHC doesn't seem to export debugging symbols at the source level? Also, based on what you've heard, would you recommend the Linux 2.6.31 performance counter tools over the PAPI library? (I see that there is PAPI support in the GHC runtime: http://hackage.haskell.org/trac/ghc/wiki/PAPI) Thanks so much for all your help! Henry