On Wed, Oct 24, 2012 at 12:16 PM, Andre Oppermann <an...@freebsd.org> wrote:
<snip> > > > See also the discussion on svn-src-all regarding global struct mtx > alignment. > > Thank you for proving my point. ;) > > Let's go back and see how we can do this the sanest way. These are > the options I see at the moment: > > 1. sprinkle __aligned(CACHE_LINE_SIZE) all over the place > 2. use a macro like MTX_ALIGN that can be SMP/UP aware and in > the future possibly change to a different compiler dependent > align attribute > 3. embed __aligned(CACHE_LINE_SIZE) into struct mtx itself so it > automatically gets aligned in all cases, even when dynamically > allocated. > > Personally I'm undecided between #2 and #3. #1 is ugly. In favor > of #3 is that there possibly isn't any case where you'd actually > want the mutex to share a cache line with anything else, even a data > structure. I've run my same tests with #3 as you describe, and I did see further noticeable improvement. I had a difficult time though quantifying the effect it would have on all of the different architectures. Putting it in ULE's tdq gained 60-70% of the overall benefit, and was well contained. I agree that sprinkling all over the place isn't pretty. But focused investigations into specific locks (spin mutexes, default mutexes, whatever) may find a few key additional ones that would benefit. I started down this path with the sleepq and turnstile locks, but none of those specifically showed noticeable improvement (at least in the tests I was running). There's still some additional ones I want to look at, but haven't had the time yet. Thanks, -Jim _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"