On Thu, May 31, 2007 at 02:57:27PM +0200, Carsten Otte wrote: > Rusty Russell wrote: > > Example block driver using virtio. > > > > The block driver uses outbufs with sg[0] being the request information > > (struct virtio_blk_outhdr) with the type, sector and inbuf id. For a > > write, the rest of the sg will contain the data to be written. > > > > The first segment of the inbuf is a result code (struct > > virtio_blk_inhdr). For a read, the rest of the sg points to the input > > buffer. > > > > TODO: > > 1) Ordered tag support. > Implementing a do_request function has quite a few disadvantages over > hooking into q->make_request_fn. This way, we have the device plug > (latency), request merging, and I/O scheduling inside the guest. > It seems preferable to do that in the host, especially when requests > of multiple guests end up on the same physical media (shared access, > or partitioned).
This kind of a claim needs some benchmark data to document it. I'll make the counterclaim that you *should* be doing I/O scheduling in the guest, both to be able to test new I/O schedulers, and to provide a set of pre-scheduled I/Os so the host has to do less work. If someone really needs the host to be doing I/O scheduling, and not the guest, then why are they using virtualization in the first place? ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kvm-devel
