On Thu, Sep 11, 2014 at 11:04:11AM +0100, One Thousand Gnomes wrote: > > > Is *that* what we are talking about? I was added to this conversation > > > in the middle where it had already generalized, so I had no idea. > > > > No, this is just what brought this craziness to my attention. > > None of it is craziness. It's the real world leaking into the crazy > delusional world of sequential programming. Machines are going to get > more not less parallel. Amen to that!!! > > For example, byte- and short-sized circular buffers could not possibly > > be safe either, when the head nears the tail. > > > > Who has audited global storage and ensured that _every_ byte-sized write > > doesn't happen to be adjacent to some other storage that may not happen > > to be protected by the same (or any) lock? > > Thats a meaningless question. Have you audited it all for correctness of > any other form. Have you mathematically verified the functionality as a > set of formal proofs ? If you can't prove its formally mathematically > functionally correct why are you worried about this ? > > Alpha works, maybe it has a near theoretical race on that point. It's not > any worse than it was 15 years ago and nobody has really hit a problem > with it. So from that you can usefully infer that those buffer cases are > not proving a real problem. Fair enough, I guess. But Alpha's limitations were given as a reason to restrict smp_store_release() and smp_load_acquire() from providing one-byte and two-byte variants. Of course, I am OK "probabilistically supporting" pre-EV56 Alpha CPUs, but only if they don't get in the way of us doing smp_store_release() and smp_load_acquire() on chars and shorts. So if pre-EV56 support has to go in order to allow smp_store_release() and smp_load_acquire() on small data types, then pre-EV56 support simply has to go. Alternatively, one way to support this old hardware on a more deterministic basis is to make the compiler use ll/sc sequences to do byte and short accesses. That would be fine as well. Thanx, Paul > The tty locks together on the other hand are asking to hit it, and the > problem you were trying to fix were the ones that need set_bit() to make > the guarantees. > > Alan > -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
