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xen-devel
Re: [Xen-devel] Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console
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To: |
Ingo Molnar <mingo@xxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Subject: |
Re: [Xen-devel] Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure for Xen console |
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From: |
Keir Fraser <keir@xxxxxxxxxxxxx> |
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Date: |
Fri, 16 Mar 2007 09:28:41 +0000 |
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Cc: |
Zachary Amsden <zach@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> |
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Fri, 16 Mar 2007 02:27:55 -0700 |
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[Xen-devel] Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure for Xen console |
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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
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