Thanks to testing from several people we seem to be narrowing down on
which debug options are causing the biggest performance hit in rawhide
kernels. As of right now, SLUB_DEBUG is the worst offender.
Fortunately, you can disabled that via the slub_debug=- command line
switch. The other option that causes a big hit is PROVE_RCU, but by
itself it isn't a major issue. Combined with SLUB_DEBUG though, it will
really impact things.
I've started collecting some of these test results here:
I'll continue to update that as people provide results.
As a note, the 3.8-rc6 kernel will not have debug options disabled. We
really only have a few major options left to get through, so we'll
continue with turning them on. The nodebug rawhide repo will contain a
build without the debug options set as usual. I expect that -rc7 will
go back to the normal method of doing things.
If you have questions/comments please drop us a line on the list!