On 2010-03-06 12:42 +0000 (Sat), Simon Marlow wrote: > Usually I find keeping the nursery size (-A) close to the L2 cache size > works best, although sometimes making it really big can be even better.
Interesting to know. I got the impression that I was being encouraged to keep -A closer to the L1 cache size, myself. > -qg disables parallel GC completely. This is usually terrible for > locality, because every GC will move all the recently allocated data > from each CPU's L2 cache into the cache of the CPU doing GC, where it > will have to be fetched out again after GC. I've since explained to Cranshaw (we are getting to have *way* too many 'Simon's around here) about the issues with our different machines; some of this depends on the host on which we're doing the testing. * Our Core i7 hosts share 8 MB of L3 cache amongst four cores with two threads each. Thus, no locality penalties here. * Our Xeon E5420 host has two 4-core CPUs, and each pair of cores shares a 6 MB L2 cache. Thus there's a pretty good chance that something you need is in someone else's cache. I don't know if there's any difference between moving stuff between two caches on the same CPU and two caches on different CPUs. * Our Xeon E5520 host has two 4-core CPUs, each core of which has two threads. Each CPU (4 cores) shares an 8 MB L3 cache. Thus, presumably, less locality penalty than the E5420 but more than an i7. As a side note, I also see slightly less memory bandwidth on this system (for both caches and main memory) than I do on an i7. This gets complex pretty fast. And don't ask me about Intel's new style of having L1 and L3 or L2 and L3 caches rather than L1 and L2 caches. > -qb disables load-balancing in the parallel GC, which improves locality > at the expense of parallelism, usually I find it is an improvement in > parallel programs. I'd think so too. Figuring out what went on here is going to have to wait until I get more detailed GC information in the eventlog. Followups to glasgow-haskell-us...@haskell.org. cjs -- Curt Sampson <c...@cynic.net> +81 90 7737 2974 http://www.starling-software.com The power of accurate observation is commonly called cynicism by those who have not got it. --George Bernard Shaw _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe