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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: |
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: |
Ingo Molnar <mingo@xxxxxxx> |
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Date: |
Fri, 16 Mar 2007 10:58:51 +0100 |
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Cc: |
Zachary Amsden <zach@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, 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 02:58:35 -0700 |
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* Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx> wrote:
> 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.
then use rmb()/wmb(). Rarely does a ring protocol truly need mb().
Ingo
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