On Wed, Jun 24, 2015 at 11:08:43AM +0000, Li, Liang Z wrote: > > > >> >> > Right now, we don't have an interface to detect that cases and > > > >> >> > got back to the iterative stage. > > > >> >> > > > >> >> How about go back to the iterative stage when detect that the > > > >> >> pending_size is larger Than max_size, like this: > > > >> >> > > > >> >> + /* do flush here is aimed to shorten the VM > > > >> >> downtime, > > > >> >> + * bdrv_flush_all is a time consuming operation > > > >> >> + * when the guest has done some file writing */ > > > >> >> + bdrv_flush_all(); > > > >> >> + pending_size = qemu_savevm_state_pending(s->file, > > max_size); > > > >> >> + if (pending_size && pending_size >= max_size) { > > > >> >> + qemu_mutex_unlock_iothread(); > > > >> >> + continue; > > > >> >> + } > > > >> >> ret = > > > >> >> vm_stop_force_state(RUN_STATE_FINISH_MIGRATE); > > > >> >> if (ret >= 0) { > > > >> >> qemu_file_set_rate_limit(s->file, > > > >> >> INT64_MAX); > > > >> >> > > > >> >> and this is quite simple. > > > >> > > > > >> > Yes, but it is too simple. If you hold all the locks during > > > >> > bdrv_flush_all(), your VM will effectively stop as soon as it > > > >> > performs the next I/O access, so you don't win much. And you > > > >> > still don't have a timeout for cases where the flush takes really > > > >> > long. > > > >> > > > >> This is probably better than what we had now (basically we are > > "meassuring" > > > >> after bdrv_flush_all how much the amount of dirty memory has > > > >> changed, and return to iterative stage if it took too much. A > > > >> timeout would be better anyways. And an interface te start the > > > >> synchronization sooner asynchronously would be also good. > > > >> > > > >> Notice that my understanding is that any proper fix for this is 2.4 > > material. > > > > > > > > Then, how to deal with this issue in 2.3, leave it here? or make an > > > > incomplete fix like I do above? > > > > > > I think it is better to leave it here for 2.3. With a patch like this > > > one, we improve in one load and we got worse in a different load > > > (depens a lot in the ratio of dirtying memory vs disk). I have no > > > data which load is more common, so I prefer to be conservative so late > > > in the cycle. What do you think? > > > > I agree, it's too late in the release cycle for such a change. > > > > Kevin > > Hi Juan & Kevin, > > I have not found the related patches to fix the issue which lead to long VM > downtime, how is it going?
Kevin is on vacation and QEMU is currently in 2.4 soft freeze. Unless patches have been posted/merged that I'm not aware of, it is unlikely that anything will happen before QEMU 2.4 is released. Stefan
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