Il 08/01/2013 14:18, Liu Yuan ha scritto: > Maybe not for a second thought. See following combination: > > cache flags WCE toggled and resulting behavior > writethrough writethrough > writeback writetrhough (writeback + flush as expected) > > cache flags means specify 'cache=xxx' at startup and WCE toggled on the > fly in the guest (supose guest kernel support WCE control) > > So the result is *not* broken. If we set cache=writethrough for > sheepdog, then WCE won't take any effect because 'flush' request will be > ignored by Sheepdog driver. And with cache=writeback, WCE does disable > the writecache and actually turns it to a writethrough cache by sending > flush req every time for write. > > To conclude, let Sheepdog interpret cache flags won't cause trouble even > with current Guest WCE feature, the different is that if we set > cache=writethrough, guest can't change it via WCE toggling. Is this > behavior acceptable?
But why is it useful to force-disable writeback caching? Do you have any performance numbers? Paolo
