GHC benchmarks

[Simon Marlow]

Ketil Malde wrote:
> Simon Marlow <simonmarhaskell at gmail.com> writes:
> 
>> Not so much code size, but data size (heap size, to be more
>> precise).
> 
> Of course.
> 
> There was some talk about storing tags in pointers for 6.8, I couldn't
> find the reference, but I wonder if that would help my situation?

Unfortunately not, the pointer-tagging optimisation doesn't affect space 
usage, only runtime.

>> It would be interesting to know how much time is spent in the GC - run
>> the program with +RTS -sstderr.
> 
> MUT time decreases a bit (131 to 127s) for x86_64, but GC time
> increases a lot (98 to 179s). 

Right - GC time doubled, which is what we'd expect to see when the resident 
data size doubles.  The decrease in MUT time is probably due to the extra 
registers available, but MUT time would also be affected by the increase in 
data size, because the cache hit rate should be lower.  On the whole, I 
think these results are to be expected.

There isn't much we can do to improve things in the short term, I'm afraid. 
  Improvements in the pipeline will hopefully enable us to make better use 
of the extra registers on x86_64, and perhaps parallel GC in the future 
will get that GC time down again.

Cheers,
	Simon