Re: [Lse-tech] Re: RFC: patch to allow lock-free traversal of lists with insertion

Ivan Kokshaysky
2001-10-10T13:25:28Z

On Wed, Oct 10, 2001 at 04:05:02AM +0200, Andrea Arcangeli wrote:
> So before changing any code, I would prefer to double check with the
> current alpha architects that the read dependency really isn't enough to
> enforce read ordering without the need of rmb also on the beleeding edge
> ev6/ev67/etc.. cores. So potentially as worse we'd need to redefine
> wmb() as wmbdd() (and friends) only for EV5+SMP compiles of the kernel,
> but we wouldn't be affected with any recent hardware compiling for
> EV6/EV67. Jay, Peter, comments?

21264 Compiler Writer's Guide [appendix C] explicitly says that the
second load cannot issue if its address depends on a result of previous
load until that result is available. I refuse to believe that it isn't
true for older alphas, especially because they are strictly in-order
machines, unlike ev6.

I suspect some confusion here - probably that architect meant loads
to independent addresses. Of course, in this case mb() is required
to assure ordering.

Ivan.