On Fri, 20 May 2011 02:10:07 +0300, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > OK, here is the large patchset that implements the virtio spec update > that I sent earlier (the spec itself needs a minor update, will send > that out too next week, but I think we are on the same page here > already). It supercedes the PUBLISH_USED_IDX patches I sent > out earlier. > > What will follow will be a patchset that actually includes 4 sets of > patches. I note below their status. Please consider for 2.6.40, at > least partially. Rusty, do you think it's feasible? Erk. I'm still unsure that we should be using ring capacity as the thresholding mechanism, given that *descriptor* exhaustion is what we actually face. That said, I will review these thoroughly in 14 hours (Sat morning my time). Perhaps I can convince myself that it's not a problem, because it *is* simpler... > List of patches and what they do: > > I) With the first patchset, we change virtio ring notification > hand-off to work like the one in Xen - > each side publishes an event index, the other one > notifies when it reaches that value - > With the one difference that event index starts at 0, > same as request index (in xen event index starts at 1). > > These are the patches in this set: > virtio: event index interface > virtio ring: inline function to check for events > virtio_ring: support event idx feature > vhost: support event index > virtio_test: support event index > > Changes in this part of the patchset from v1 - address comments by Rusty et al. > > I tested this a lot with virtio net block and with the simulator and esp > with the simulator it's easy to see drastic performance improvement > here: > > [virtio]# time ./virtio_test > spurious wakeus: 0x7 > > real 0m0.169s > user 0m0.140s > sys 0m0.019s > [virtio]# time ./virtio_test --no-event-idx > spurious wakeus: 0x11 > > real 0m0.649s > user 0m0.295s > sys 0m0.335s > > And these patches are mostly unchanged from the very first version, > changes being almost exclusively code cleanups. So I consider this part > the most stable, I strongly think these patches should go into 2.6.40. > One extra reason besides performance is that maintaining > them out of tree is very painful as guest/host ABI is affected. > > II) Second set of patches: new apis and use in virtio_net > With the indexes in place it becomes possibile to request an event after > many requests (and not just on the next one as done now). This shall fix > the TX queue overrun which currently triggers a storm of interrupts. > > Another issue I tried to fix is capacity checks in virtio-net, > there's a new API for that, and on top of that, > I implemented a patch improving real-time characteristics > of virtio_net > > Thus we get the second patchset: > virtio: add api for delayed callbacks > virtio_net: delay TX callbacks > virtio_ring: Add capacity check API > virtio_net: fix TX capacity checks using new API > virtio_net: limit xmit polling > > This has some fixes that I posted previously applied, > but otherwise ideantical to v1. I tried to change API > for enable_cb_delayed as Rusty suggested but failed to do this. > I think it's not possible to define cleanly. > > These work fine for me, I think they can be merged for 2.6.40 > too but would be nice to hear back from Shirley, Tom, Krishna. See other mail. > III) There's also a patch that adds a tweak to virtio ring > virtio: don't delay avail index update > > This seems to help small message sizes where we are constantly draining > the RX VQ. This is independent. If someone shows some benchmark improvement I'm definitely happy to put this in .40, if nothing else. > I'll need to benchmark this to be able to give any numbers > with confidence, but I don't see how it can hurt anything. > Thoughts? > > IV) Last part is a set of patches to extend feature bits > to 64 bit. I tested this by using feature bit 32. > vhost: fix 64 bit features > virtio_test: update for 64 bit features > virtio: 64 bit features Sweetness, but .41 material at this stage. Thanks, Rusty. -- 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
