On Tue, Jul 17, 2012 at 11:32:45AM +0200, Paolo Bonzini wrote: > Il 17/07/2012 11:21, Asias He ha scritto: > >> It depends. Like vhost-scsi, vhost-blk has the problem of a crippled > >> feature set: no support for block device formats, non-raw protocols, > >> etc. This makes it different from vhost-net. > > > > Data-plane qemu also has this cripppled feature set problem, no? > > Yes, but that is just a proof of concept. We can implement a separate > I/O thread within the QEMU block layer, and add fast paths that resemble > data-path QEMU, without limiting the feature set. > > > Does user always choose to use block devices format like qcow2? What > > if they prefer raw image or raw block device? > > If they do, the code should hit fast paths and be fast. But it should > be automatic, without the need for extra knobs. aio=thread vs. > aio=native is already one knob too much IMHO. Well one extra knob at qemu level is harmless IMO since the complexity can be handled by libvirt. For vhost-net libvirt already enables vhost automatically dependeing on backend used and I imagine a similar thing can happen here. > >> So it begs the question, is it going to be used in production, or just a > >> useful reference tool? > > > > This should be decided by user, I can not speak for them. What is wrong > > with adding one option for user which they can decide? > > Having to explain the user about the relative benefits; This can just be done automatically by libvirt. > having to > support the API; having to handle transition from one more thing when > something better comes out. > > Paolo Well this is true for any code. If the limited featureset which vhost-blk can accelerate is something many people use, then accelerating by 5-15% might outweight support costs. -- 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
