Amitayu Das
2006-Mar-27 16:57 UTC
[Xen-devel] Scheduling questions for I/O activity on Dom0
Hi, I had a quick question. Whenever a DomU wants to transmit/receive, it needs Dom0 to work on behalf of it to do the needful. Now, I''m confused about the way no. of packets are transmitted (the next para will make the things clearer). Consider the different options noted below and tell me which one is correct. 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? Thanks, Amitayu _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Mark Williamson
2006-Mar-27 17:01 UTC
Re: [Xen-devel] Scheduling questions for I/O activity on Dom0
> 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! _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel