On Mon, 2014-01-06 at 19:29 -0800, Davidlohr Bueso wrote: > On Mon, 2014-01-06 at 12:52 -0800, Darren Hart wrote: > > On Thu, 2014-01-02 at 07:05 -0800, Davidlohr Bueso wrote:
> > I thought someone, Peter Z?, had commented on these CONFIG_SMP bits. Are > > they really necessary? Does smp_mb__after_atomic_inc() and smp_rmb() not > > already just do the right thing as far as we're concerned here? > > I don't think so. Thomas and I agreed that this was in fact the way to > go. I rechecked old email and didn't notice any objections to > CONFIG_SMP. Also for things like hb_waiters_pending we definitely need > it. I'll happily defer to Thomas here. > > > > Given the subtlety of the implementation - I think it would be good to > > explicitly annotate the get_futex_key() call site in futex_wake() as > > providing the MB (B). > > > > Similar comment for futex_wait() and futex_requeue() for MB (A). > > > > These will also raise the appropriate red flags for people looking to > > optimize or modify these paths in the future. It would be good to have > > it in the top level futex_* function to make the MB placement and > > relationship explicitly clear. > > > > Something quite similar was already there for v2 but PeterZ's feedback > made me update the main documentation at the top of futex.c to as it is > now... I don't want to block this any longer - but as complicated and non-obvious as this is, I would *MUCH* prefer we document the memory barrier point in the top level algorithm. If Peter/Thomas/Linus/Ingo object, so be it, but otherwise let's err on the side of overly explicit documentation. Peter/Thomas/Linus/Ingo: Do any of you object to adding the three memory barrier comments to the high level functions? futex_wait, futex_wake, futex_requeue? -- Darren Hart Intel Open Source Technology Center Yocto Project - Linux Kernel -- 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/
