On Sun, Oct 27, 2013 at 11:00:33AM +0200, Victor Kaplansky wrote: > Peter Zijlstra <pet...@infradead.org> wrote on 10/25/2013 07:37:49 PM: > > > I would argue for: > > > > READ ->data_tail READ ->data_head > > smp_rmb() (A) smp_rmb() (C) > > WRITE $data READ $data > > smp_wmb() (B) smp_mb() (D) > > STORE ->data_head WRITE ->data_tail > > > > Where A pairs with D, and B pairs with C. > > 1. I agree. My only concern is that architectures which do use atomic > operations > with memory barriers, will issue two consecutive barriers now, which is > sub-optimal.
Yeah, although that would be fairly easy to optimize by the CPUs itself; not sure they actually do this though. But we don't really have much choice aside of introducing things like: smp_wmb__after_local_$op; and I'm fairly sure people won't like adding a ton of conditional barriers like that either. > 2. I think the comment in "include/linux/perf_event.h" describing > "data_head" and > "data_tail" for user space need an update as well. Current version - Oh, indeed. Thanks; I'll update that too! -- 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/
