Rusty Russell wrote: > On Tue, 2007-07-17 at 23:49 -0700, Dor Laor wrote: > >>> On Tue, 2007-07-17 at 06:31 -0700, Dor Laor wrote: >>> >>>> btw: Rusty - what do you think of virtio for the host? >>>> >>> You mean backend? For networking it makes a great deal of sense. For >>> block it makes far less sense (COW, weird formats, etc). >>> >> I meant networking, but there are more components we can add to the >> host: >> - Block device can be directed into blkTap thus making the >> result both flexible and zero-copy. >> > > Let's avoid the term "zero-copy" since it usually indicates that the > people in the discussion can't count.
Well, for block you can do zero copy, using O_DIRECT. > Let's further assume that kvm > changes to the lguest model where guest pages are user pages. > That's a valid assumption. The rest of the discussion doesn't depend on it, does it? > AFAICT the only difference between a userspace host block driver and a > kernel host block driver is now the system call overhead, and the > difficulty of doing efficient write barriers from userspace. > > True. For mortal people setups where you have at most a few thousand ops/sec, the overhead is negligible. In-kernel host drivers make sense only for 100+ disks. These people are better off using blockdevs rather than file, so an in-kernel block device need not support file-based storage. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- 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 kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
