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Date: Sat, 08 Dec 2007 15:59:19 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Re: [PATCH 2/3] virtio network device
References: <4755CC8C.6000001@us.ibm.com>	<200712051744.03916.paul@codesourcery.com>	<47570817.9090908@us.ibm.com>
	<200712081322.39762.paul@codesourcery.com>
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To: qemu-devel@nongnu.org
Cc: Anthony Liguori <aliguori@us.ibm.com>, Rusty Russell <rusty@rustcorp.com.au>

Paul Brook wrote:
>> virtio makes things a bit trickier though.  There's a shared ring queue
>> between the host and guest.  The ring queue is lock-less and depends on
>> the ability to atomically increment ring queue indices to be SMP safe.
>> Using a copy-API wouldn't be a problem for QEMU since the host and guest
>> are always running in lock-step.  A copy API is actually needed to deal
>> with differing host/guest alignment and endianness.
>>     
>
> That seems a rather poor design choice, as many architectures don't have an 
> atomic increment instruction. Oh well.
>   

Sorry, I should have been more clear.  An atomic increment isn't needed, 
just an atomic store.

Regards,

Anthony Liguori

> Paul
>
>
>
>