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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>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx> |
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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 10:31:49 +0000 |
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Cc: |
xen-devel@xxxxxxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> |
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Fri, 16 Mar 2007 03:31:03 -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 09:58, "Ingo Molnar" <mingo@xxxxxxx> wrote:
>> 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.
>
> then use rmb()/wmb(). Rarely does a ring protocol truly need mb().
It's needed for writing data /after/ reading the consumer index that shows
you have space to write. Looking through xenbus_comms.c I think all the
barriers are correct except there is a spurious extra mb() in xb_read(),
where there is a later rmb() which is sufficient by itself. All the others
have a purpose.
-- Keir
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