[rust-dev] Weird performance regression in 0.7?

Tommy M. McGuire mcguire at crsr.net
Sat Jul 6 08:37:49 PDT 2013

When I updated my idiotic anagrams-hashmap toy to 0.7, I seem to have
run across a weird performance regression involving hashmaps.

Previous runs took approximately 6 seconds, but the 0.7 build is 1)
taking about 35 seconds and 2) very variable, since rebuilding it and
sometimes just running it several more times results in smaller run
times of ~22 seconds. Further, inserting some println's to look at what
was taking so long reduced the run time to about 9 seconds.

It is not limited to that particular program; other versions seem to be
affected as well, including anagrams-hashmap-mmap, which was just
recently run with a post-incoming-change build of the master branch. (5
seconds vs. 11 seconds.)

Any ideas what is going on?


Tommy M. McGuire
mcguire at crsr.net

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