Re: [PATCH RFC 1/3] virtio infrastructure

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Rusty Russell wrote:
>   
>> Networking hardware generally services descriptors in a FIFO manner.
>>     
>
> Well, ethernet guarantees order.  Not sure about others tho...
>
>   

OT: Does that hold for bonded interfaces too?

>> virtio may not (for example, it may offload copies of larger packets to 
>> a dma engine such as I/OAT, resulting in a delay, but copy smaller 
>> packets immediately).  that means that there will be some mismatch 
>> between virtio drivers and real hardware drivers.
>>     
>
> I think your point is that the completion bitmap (or indeed, the current
> approach) does not maintain order?  Hmm, this is more convincing to me
> than cache arguments, since some devices might want ordering and want
> more than a single io in flight.
>   

Well, it wasn't really; sorry for being unclear.  My point was that 
virtio interfaces will not match hardware exactly.

My objection is to "scan all slots, occupied or not, for completion".  I 
think virtio should present completed descriptors without the need for 
scanning, even if it means looking a bit different from a typical 
ethernet driver.


-- 
error compiling committee.c: too many arguments to function


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