Samuel Bronson wrote:
Oops. I accidentally sent this just to SPJ... sorry!
On 10/31/06, Simon Peyton-Jones <[EMAIL PROTECTED]> wrote:
Sam
How to progress? Rather than try to follow the detailed path of your
investigation, I wonder if you might do the following. When you achieve
a stable situation where you think you have a collection of
modifications that improve at least some programs, without making any
significantly worse (you can negotiate about exceptions) send a patch or
patches (to GHC and the libraries) that implements your proposal, along
with a summary of what they do (unless that's all clear from the patch
messages themselves). Preferably without patches that do X and later
undo X...
That way Simon and Ian and I can review and test one thing. Does that
make sense?
Yeah. I've been under the impression that that was going to have to
happen before my patches were applied, I've basically just been hoping
for tips. Or "oh god no, don't do that! do this instead!" or
something. I've been working with a definition of "significant" where
1% slower doesn't count, but 5% does. And I've been assuming that a 1%
all-around increase in code size isn't too bad. And lately (since the
patch that doesn't consider unlifted args interesting unless they are
literals), I haven't seen *any* changes in allocation from my
unpatched tree. Hopefully with my patch to build the libraries with
-fext-core I will actually be able to figure out what is going on in
the libraries (which seems to be where a lot of the differences that
matter are). I assume there aren't really any performance
considerations there ;-).
I find the instruction counts and memory read/write counts from cachegrind are
good things to compare, as a slightly more sensitive, but still deterministic,
alternative to allocations. Caveats apply of course - these figures are not
always a good indicator for real world performance, but they are still a useful
tool if you bear this in mind.
Cheers,
Simon
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