Michael, What's you have suggested could avoid to taint the guest virtio-net driver. Really thanks! For the two alternative, the first will do more trick with driver or net-core stuff. So currently, I prefer to try the second one. Anyway, let me have a good think of it. Thanks! Thanks Xiaohui >-----Original Message----- >From: kvm-owner@xxxxxxxxxxxxxxx [mailto:kvm-owner@xxxxxxxxxxxxxxx] On Behalf Of >Michael S. Tsirkin >Sent: Thursday, May 27, 2010 4:20 PM >To: Xin, Xiaohui >Cc: netdev@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Herbert >Xu >Subject: Re: issue about virtio-net driver to suppoprt vhost mergeable buffer with zero-copy >to support PS mode > >On Thu, May 27, 2010 at 09:21:02AM +0800, Xin, Xiaohui wrote: >> Michael, >> I'm now looking into the vhost mergeable buffer, and I tried to use it to support PS mode >with zero-copy. And I found an issue there that I have to modify the guest virito-net driver. >> >> When guest virtio-net driver submits mergeable buffers, it submits multiple pages outside. >In zero-copy case, vhost cannot know which page is used to put header, and which page is >used to put payload. Then vhost can only reserves 12 bytes for each page. That means, the >page_offset of the payload DMAed into the guest buffer is always 12 bytes. But guest >virtio-net driver always use offset 0 to put the data (See receive_mergeable()). That's where >the zero-copy use mergeable buffer must modify. >> >> Have I missed something here? And how do you think about it? >> >> Thanks >> Xiaohui > >Maybe you can teach the hardware skip the first 12 bytes: qemu will >call an ioctl telling hardware what the virtio header size is. >This is how we plan to do it for tap. > >Alternatively, buffers can be used in any order. >So we can have hardware use N buffers for the packet, and then >have vhost put the header in buffer N+1. > >-- >MST >-- >To unsubscribe from this list: send the line "unsubscribe kvm" in >the body of a message to majordomo@xxxxxxxxxxxxxxx >More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
