On Fri, Sep 20, 2013 at 11:08:06AM +0100, Will Deacon wrote: > On Thu, Sep 19, 2013 at 07:11:32PM +0100, Linus Torvalds wrote: > > From a performance standpoint, lockref really is expected to mainly > > help with big machines. Only insane people would do big machines with > > 32-bit kernels these days. > > Our definitions of "big" machines probably differ significantly, but it > would be interesting to see if this *does* make a difference on some of the > multi-cluster ARMv7 hardware.
[...] > > In other words, I'd actually like to see some numbers if there are > > loads where this actually helps and matters... > > That's fair enough; I just saw the new lockref stuff, thought "that's a cool > hack" then looked at playing with it on ARM. I'll go see what this AIM7 > thing is all about... Right, turns out I can get some interesting numbers from your simple t.c program on my dual-cluster, 5 CPU ARMv7 machine. The new cmpxchg-based lockref code gives ~50% improvement, but the fun part is that implementing cmpxchg64 without memory barriers doubles this win to ~100% over current mainline. If we can guarantee that the CODE just messes around with the lockref, those barriers probably aren't needed... As for AIM7/re-aim, I'm having a hard time getting repeatable numbers out of it to establish a baseline, so it's not proving to be especially helpful. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
