On Tue, Aug 17, 2010 at 09:39:15AM -0500, Anthony Liguori wrote: > The type of cache we present to the guest only should relate to how > the hypervisor caches the storage. It should be independent of how > data is cached by the disk. It is. > There can be many levels of caching in a storage hierarchy and each > hierarchy cached independently of the next level. > > If the user has a disk with a writeback cache, if we expose a > writethrough cache to the guest, it's not our responsibility to make > sure that we break through the writeback cache on the disk. The users doesn't know or have to care about the caching. The users uses O_SYNC/fsync to tell it wants data on disk, and it's the operating systems job to make that happen. The situation with qemu is the same - if we tell the guest that we do not have a volatile write cache that needs explicit management the guest can rely on the fact that it does not have to do manual cache management. -- 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
