Re: [Xen-devel] Scheduling questions for I/O activity on Dom0

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> a. DomU sends 1 packet *ONLY*, waits for Dom0 to serve him. Later
> whenever, Dom0 is scheduled, it transmits that single packet; an
> inefficient way of doing the things.
>
> b. DomU sends one/multiple packets (>=1) and waits for Dom0 to serve
> him. Later Dom0 serves for him whenever Dom0 is scheduled; a more
> efficient way of doing the things.
>
> I think (b) is adopted by Xen, but am not sure. Can you guys kindly tell
> me?

Yes, that's right.

The packets (or rather, descriptors for the packets) are queued in a shared 
memory ringbuffer for dom0 to find them.

Event channels are used for dom0/domU to notify each other of changes in the 
ring.  Events are not generated for each packet for reasons of efficiency - 
batching makes virtualisation less painful (in terms of performance) for 
network devices.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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