On Mon, May 16, 2011 at 04:43:21PM +0930, Rusty Russell wrote: > On Sun, 15 May 2011 15:48:18 +0300, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > On Mon, May 09, 2011 at 03:27:33PM +0930, Rusty Russell wrote: > > > On Wed, 4 May 2011 23:52:33 +0300, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > > Add an API that tells the other side that callbacks > > > > should be delayed until a lot of work has been done. > > > > Implement using the new used_event feature. > > > > > > Since you're going to add a capacity query anyway, why not add the > > > threshold argument here? > > > > I thought that if we keep the API kind of generic > > there might be more of a chance that future transports > > will be able to implement it. For example, with an > > old host we can't commit to a specific index. > > No, it's always a hint anyway: you can be notified before the threshold > is reached. But best make it explicit I think. > > Cheers, > Rusty. I tried doing that and remembered the real reason I went for this API: capacity is limited by descriptor table space, not used ring space: each entry in the used ring frees up multiple entries in the descriptor ring. Thus the ring can't provide callback after capacity is N: capacity is only available after we get bufs. We could try and make the API pass in the number of freed bufs, however: - this is not really what virtio-net cares about (it cares about capacity) - if the driver passes a number > number of outstanding bufs, it will never get a callback. So to stay correct the driver will need to track number of outstanding requests. The simpler API avoids that. APIs are easy to change so I'm guessing it's not a major blocker: we can change later when e.g. block tries to pass in some kind of extra hint: we'll be smarter about how this API can change then. Right? -- 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
