[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure for Xen console

On 16/3/07 08:54, "Ingo Molnar" <mingo@xxxxxxx> wrote:

>> + prod = intf->in_prod;
>> + mb();
>> + BUG_ON((prod - cons) > sizeof(intf->in));
> such mb()'s are typically a sign of "i have no clear idea what SMP
> serialization rules apply here, but something is needed because
> otherwise it breaks" ?

These mb()'s are pretty standard for lock-free producer/consumer rings.
Write descriptor /then/ write the updated producer. Read the producer /then/
read any descriptors revealed by this new producer value.

All our ring protocols (and we have a few) require memory barriers. Those
that use our standard set of ring macros have the memory barriers hidden
from view, but they're still there.

 -- Keir

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.