| Posted | Nick | Remark | |
|---|---|---|---|
| #openstack-nova - 2017-02-01 | |||
| 10:12:47 | gmann | johnthetubaguy: alex_xu btw do we have meeting today? do not think alex_xu is back | |
| 10:13:55 | johnthetubaguy | gmann: I don't know if we decided something, given its crazy o'clock for your all, I vote we skip it, but I will try start the meeting in case folks are about and want to discuss things | |
| 10:15:33 | gmann | ok | |
| 10:20:12 | kashyap | raj_singh: Hi, you have assigned someone to work on this -- https://bugs.launchpad.net/nova/+bug/1605016 | |
| 10:20:12 | openstack | Launchpad bug 1605016 in OpenStack Compute (nova) "Post copy live migration interrupts network connectivity" [High,In progress] - Assigned to Sivasathurappan Radhakrishnan (siva-radhakrishnan) | |
| 10:20:18 | cdent | gmann, johnthetubaguy: If we're talking about api meetings I'd vote for skip too | |
| 10:20:31 | kashyap | Do they have requisite knowledge to work on it? Or should I reassign the bug back to 'nodbody'? | |
| 10:22:42 | gmann | cdent: yea, api meeting. me too to skip. | |
| 10:27:20 | johnthetubaguy | kashyap: we are training him up, he is struggling a bit on it though | |
| 10:27:53 | kashyap | johnthetubaguy: Me nods. That bug is quite complicated. Maybe a lower-hanging fruit might be better? | |
| 10:27:57 | johnthetubaguy | kashyap: he is testing out the fix in an environment at the moment I believe | |
| 10:28:05 | kashyap | johnthetubaguy: I say that because, right now QEMU migration devs are asking: What is Nova's stance on postcopy | |
| 10:28:13 | kashyap | So, I lost complete memory of it | |
| 10:28:19 | kashyap | Maybe mdbooth can shed some light there? | |
| 10:28:33 | johnthetubaguy | kashyap: support is in, works with majority of neutron back ends, but not all, AFAIK | |
| 10:29:06 | johnthetubaguy | we discussed it alot at the summit, and siva_krishnan is implementing what we agreed would be the "quick fix", calling neutron earlier in the process | |
| 10:29:41 | mdbooth | johnthetubaguy: IIRC the problem with that change wasn't so much working out what needed to be done, as finding somebody with enough arcane neutron knowledge to know which backends allowed it to be done. | |
| 10:29:49 | johnthetubaguy | would love to trigger of QEMU events to get more exact timing of when the post copy occurs, but the basic structure is going in the above change | |
| 10:30:23 | johnthetubaguy | mdbooth: I am confused then, neutron folks agreed this should be OK at the summit, what changed from that? | |
| 10:30:32 | mdbooth | johnthetubaguy: The qemu events things isn't required at all in this instance, because the change happens synchronously on the source. | |
| 10:30:41 | kashyap | johnthetubaguy: I have asked David Gilbert of QEMU to join here. He can ask questions to his heart's content, and he goes out of his way to explain | |
| 10:30:44 | davidgiluk | kashyap: nod | |
| 10:30:54 | kashyap | davidgiluk: Ah, you are here :-) | |
| 10:30:55 | mdbooth | i.e. there's no need to respond to an event from a call which you just made in code you're still executing | |
| 10:31:00 | johnthetubaguy | mdbooth: I keep being told its not syncronus | |
| 10:31:13 | mdbooth | What's not synchronous about it? | |
| 10:31:19 | johnthetubaguy | you just say, please do post copy at end of next iterration, I believe | |
| 10:31:30 | johnthetubaguy | so when we call post copy, it doesn't immediatly happen, I was told | |
| 10:31:31 | kashyap | davidgiluk: So, this is what johnthetubaguy was saying, when I asked him about "What is Nova's stance on postcopy": < johnthetubaguy> support is in, works with majority of neutron back ends, but not all, AFAIK | |
| 10:32:13 | johnthetubaguy | there can be a small network outage with some backends, during the post copy process (which ironically speeds up the live-migrate, of course) doing work to avoid that | |
| 10:32:24 | davidgiluk | kashyap: Yeh so my understanding was it was waiting on a fix to lp 1605016 for the others, with https://review.openstack.org/#/c/413021/9 being a proposed fix | |
| 10:32:24 | openstack | Launchpad bug 1605016 in OpenStack Compute (nova) "Post copy live migration interrupts network connectivity" [High,In progress] https://launchpad.net/bugs/1605016 - Assigned to Sivasathurappan Radhakrishnan (siva-radhakrishnan) | |
| 10:32:24 | mdbooth | johnthetubaguy: In _live_migration_monitor we do: | |
| 10:32:32 | mdbooth | if (is_post_copy_enabled and | |
| 10:32:32 | mdbooth | libvirt_migrate.should_switch_to_postcopy( | |
| 10:32:32 | mdbooth | info.memory_iteration, info.data_remaining, | |
| 10:32:32 | mdbooth | previous_data_remaining, migration.status)): | |
| 10:32:32 | mdbooth | libvirt_migrate.trigger_postcopy_switch(guest, | |
| 10:32:33 | mdbooth | instance, | |
| 10:32:35 | mdbooth | migration) | |
| 10:32:51 | johnthetubaguy | mdbooth: its the libvirt call that I am told is async | |
| 10:33:07 | johnthetubaguy | mdbooth: it just request post copy at some point in the future, and returns right away, before actually triggering it | |
| 10:33:12 | mdbooth | johnthetubaguy: Well we might switch a few milliseconds early | |
| 10:33:16 | johnthetubaguy | mdbooth: pkoniszewski has the details on that | |
| 10:33:19 | mdbooth | Rather than a few milliseconds late | |
| 10:33:39 | johnthetubaguy | mdbooth: I was told more like seconds, but yeah, I was betting on milliseconds myself | |
| 10:33:46 | davidgiluk | the postcopy transition happens at the end of a pass, and libvirt gets involved before starting the destination | |
| 10:34:03 | johnthetubaguy | mdbooth: either way, I vote for the approach siva_krishnan has in the works already, just need to iron things out | |
| 10:34:12 | johnthetubaguy | davidgiluk: sorry, whats waiting on the fix/ | |
| 10:34:23 | johnthetubaguy | s/ / / ? / | |
| 10:34:32 | davidgiluk | johnthetubaguy: The support for other networking configs | |
| 10:35:05 | johnthetubaguy | davidgiluk: that bug fix should help reduce the network outage some networking configs currently see, yes | |
| 10:35:43 | davidgiluk | johnthetubaguy: < johnthetubaguy> would love to trigger of QEMU events to get more exact timing of when the post copy occurs, but the basic structure is going in the above change | |
| 10:35:48 | davidgiluk | johnthetubaguy: We already emit the events | |
| 10:36:20 | johnthetubaguy | davidgiluk: agreed its omitted, we first need all the structures in place to call neutron at the right time, the current patch | |
| 10:36:34 | johnthetubaguy | oops emitted | |
| 10:36:43 | davidgiluk | generate :-) | |
| 10:37:32 | mdbooth | Well, this merged: https://review.openstack.org/#/c/402318/ :( | |
| 10:37:49 | mdbooth | The libvirt driver becomes slightly less fathomable for no appreciable gain. | |
| 10:38:11 | davidgiluk | johnthetubaguy: you should probably loop in jdenemar to check what it looks like for you from ontop of libvirt - but you should have all the events you need to know when postcopy kicks in | |
| 10:38:35 | kashyap | mdbooth: Propose a revert? | |
| 10:38:47 | johnthetubaguy | davidgiluk: thats the plan for the follow up fix | |
| 10:38:54 | mdbooth | kashyap: I proposed not merging it, which didn't work. | |
| 10:39:01 | kashyap | mdbooth: From glancing at your comments on the review | |
| 10:39:06 | davidgiluk | johnthetubaguy: OK, great; if you do need anything more from qemu, just ask | |
| 10:39:09 | johnthetubaguy | mdbooth: sorry, got pulled into meetings after that one, so I didn't get chance to delay it | |
| 10:39:10 | kashyap | mdbooth: No one has bothered to respond with a counter-argument | |
| 10:39:17 | johnthetubaguy | mdbooth: I can fast revert it if you want | |
| 10:39:36 | kashyap | Then, you have by all means, a right to revert it, and restart the discussion, and make whoever proposed it to respond | |
| 10:39:48 | mdbooth | johnthetubaguy: If you wouldn't mind. I'm assuming, btw, that there are no real users being impacted by this. | |
| 10:40:40 | johnthetubaguy | mdbooth: no idea, the SUSE folks proposed this, and I believe they support users on Xen + Libivrt + Nova, so I was assuming yes | |
| 10:41:15 | mdbooth | It's been broken forever though, right? | |
| 10:41:36 | johnthetubaguy | mdbooth: sure, I assumed they were trying to change that for one of their users that are complaining | |
| 10:42:09 | mdbooth | I just don't want to add more sticky tape without investigating fixing the root cause. | |
| 10:42:25 | mdbooth | I don't see any evidence anybody looked for the root cause. | |
| 10:43:17 | johnthetubaguy | mdbooth: I added my assumption of the cause in the review, well the root cause is Xen being very picky about the device names | |
| 10:43:55 | mdbooth | We need to either be picky earlier, or translate it earlier. | |
| 10:44:18 | johnthetubaguy | mdbooth: the problem is, you don't know if its Xen until it hits the compute node | |
| 10:44:19 | mdbooth | Sticking a band-aid at the lowest possible level is just going to be a source of bugs | |
| 10:44:42 | mdbooth | Yeah, that occurred to me. No immediate answer to that as I haven't given it any thought. | |
| 10:44:53 | mdbooth | Seems that nobody else has either, though. | |
| 10:45:46 | mdbooth | Might be something to be resolved in driver.spawn, and attach/detach volume? | |
| 10:46:03 | mdbooth | That way it's resolved at the time it's created | |
| 10:47:55 | mdbooth | Do those names have any semantic meaning at the api level beyond 'the Nth disk' anyway? I don't think we support multiple controller types, do we? | |
| 10:48:24 | johnthetubaguy | we support multiple hypervisors in a single cloud, at least in theory | |
| 10:48:38 | mdbooth | If ^^^ is a valid assumption, ComputeManager could rewrite it to a number, and the driver could change it back to whatever it wanted. | |
| 10:48:58 | johnthetubaguy | I don't think we even respect the number any more, but it could | |
| 10:49:01 | mdbooth | johnthetubaguy: It's in a single instance. i.e. could we have both sda and vda in the same instance? | |
| 10:49:36 | johnthetubaguy | sda would always fail to attach, all disks need to be vd* I believe, or xvd* | |
| 10:50:17 | mdbooth | Right, so computemanager would see it got 'sda' from the api, translate that to '0', and the driver would change it to 'sda', 'vda', or 'xvda' as required. | |
| 10:51:08 | johnthetubaguy | seems like a good refactor to do on top of the bug fix | |
| 10:51:54 | mdbooth | johnthetubaguy: The bug fix makes the existing code worse, though, and I see no evidence that anybody looked for a root cause. | |
| 10:52:47 | mdbooth | Given that it's obviously not urgent, I don't see why we would choose to take more tech debt for that. | |
| 10:53:28 | mdbooth | Anyway, it's not that important in itself. | |
| 10:53:44 | mdbooth | Just death by 1,000 cuts. | |
| 10:53:55 | johnthetubaguy | it breaks a pretty fundamental API feature, that seemed fairly important to be from a parity point of view, but I duno really. | |
| 10:56:54 | mdbooth | johnthetubaguy: Yeah, I know. But it's been broken a long time and I'd have preferred to see an attempt to fix it without adding tech debt first. | |
| 10:57:34 | johnthetubaguy | mdbooth: that my preference too, but its a balancing act | |
| 10:58:11 | johnthetubaguy | I was very boarderline on -1 +2 myself | |
| 10:58:14 | mdbooth | If it's important to somebody, they'll fix it. You even suggested where to look, and I agreed. | |