There was a recent thread on the ActiveState list which was never quite solved. In general it came down to assigning to @_ was causing some weirdness to occur and ActiveState perl 5.6.1 would slow down to a crawl after a few thousand iterations. Other perls like my OpenBSD 5.6.1 and Cygwin 5.8.0 behaved nicely.
I'm not sure what the issue was but there may be lurking bug in assigning to @_. I'm warning against it. (or at least be aware so if you do run into trouble later...)
Update: fixed some spelling