help wrt semantics / primops for pure prefetches
Simon Marlow
marlowsd at gmail.com
Thu Nov 27 09:36:41 UTC 2014
I haven't been watching this, but I have one question: does prefetching
actually *work*? Do you have benchmarks (or better still, actual
library/application code) that show some improvement? I admit to being
slightly sceptical - when I've tried using prefetching in the GC it has
always been a struggle to get something that shows an improvement, and
even when I get things tuned on one machine it typically makes things
slower on a different processor. And that's in the GC, doing it at the
Haskell level should be even harder.
Cheers,
Simon
On 22/11/2014 05:43, Carter Schonwald wrote:
> Hey Everyone,
> in
> https://ghc.haskell.org/trac/ghc/ticket/9353
> and
> https://phabricator.haskell.org/D350
>
> is some preliminary work to fix up how the pure versions of the prefetch
> primops work is laid out and prototyped.
>
> However, while it nominally fixes up some of the problems with how the
> current pure prefetch apis are fundamentally borken, the simple design
> in D350 isn't quite ideal, and i sketch out some other ideas in the
> associated ticket #9353
>
> I'd like to make sure pure prefetch in 7.10 is slightly less broken
> than in 7.8, but either way, its pretty clear that working out the right
> fixed up design wont happen till 7.12. Ie, whatever makes 7.10, there
> WILL have to be breaking changes to fix those primops for 7.12
>
> thanks and any feedback / thoughts appreciated
> -Carter
>
>
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