* Pekka Enberg <penberg@xxxxxxxxxx> wrote: > On Sat, 2011-05-07 at 16:47 +0200, Ingo Molnar wrote: > > Can you anything in the virtio protocol implementation that would explain > > networking lags, which seem to be caused by guest notifications either not be > > sent or being missed? > > > > In particular this sequence: > > > > > while pending_requests: > > > a = get_next_request(); > > > process_next_request(a); > > > > is apparently not what Qemu uses - so maybe there's some latent bug or some > > silly oversight somewhere. > > > > It is suboptimal and i agree with you that the better sequence should be > > implemented, but the above *should* work, yet it does not. > > Yes, so the performance benefits of Asias' patch aren't the interesting > part but the fact that it fixes a real bug in our tool. It could be the same like the mutex_lock() change: that too seemed to 'fix' the latency bug but we still do not understand the root cause of the 'stuck ring-buffer' situation. I.e. some sort of timing related condition which goes away spuriously when unrelated but timing-relevant changes are done to the code. And we'll continue to see these problems on and off, in probably all virtio drivers. virtio-console might be suffering from it, virtio-blk, etc. etc. I'd suggest freezing changes to this driver until this bug is analyzed correctly... Thanks, Ingo -- 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
