Marcin Juszkiewicz

During last week I was in Dublin, Ireland on OpenStack PTG. It was also the worst weather since 1982. There was snow and strong wind so conference quickly got renamed to SnowpenStack.

The main reasons for me to be there were:

• meet all those developers who took some time and looked at my changes
• discuss some other changes/plans
• share aarch64 knowledge with OpenStack projects

Conference took place in the Croke Park stadium. We used meeting rooms on 4th, 5th, 6th floors. One day by mistake I took wrong stairs and ended on top of the stadium in just T-shirt… Quickly ran to an elevator to get back to proper floor ;D

The schedule was split into two parts: Monday and Tuesday were for mixed teams sessions while Wednesday — Friday were for discussions in teams. I spoke with Kolla, Nova and Infra teams mostly. There were some discussions with Ironic, Kuryr and some other ones too. Also met several Polish developers so there was a time to speak in native language ;D

On Tuesday I went to the city centre to buy some souvenirs for family (and 99th fridge magnet for myself). Launched Ingress, did one mosaic to see more of a city and after 11 kilometres I was back at the hotel just in time for a small party in GAA museum. And then pub trip with Polish guys. When I finally reached the hotel (about 01:30) there were still discussions in the lobby and I took a part in one of them.

Team discussions started on Wednesday. Visited Nova one summarizing ‘Queens’ release. Turned out that it went better than previous ones. The main problem was lack of reviews — not everyone likes to pester developers on IRC to get some attention to patches. I was asked few times for opinion as I was one of few fresh contributors.

Kolla sessions were a bit chaotic in my opinion. Recently chosen PTL was not present and the person supposed to replace him got stuck at home due to weather. One of the discussions I remember was about Ceph: should we keep using our images or rather move to ‘ceph-ansible’ instead. Final idea was to keep as it looked like there were more cons than pros with moving to ‘ceph-ansible’ images.

Discussed Arm64 support with Infra team. We (Linaro) provided them resources on one of our developer clouds to get aarch64 present in OpenStack CI gates. Turned out that machines work and some initial tests were done. I also got informed that diskimage-builder patches to add GPT/UEFI support will be reviewed soon.

And then there were some weather related issues. On Wednesday every attendee got an email with information that Irish government issued the Red Alert which strongly suggest to stay inside if you do not really have to go outside. And as attendance was not mandatory then people should first check are they comfortable with going to Croke Park (especially those who not stayed in the hotel nearby). Next day organization team announced that the venue we used will close after lunch to make sure that everyone is safe. And the whole conference moved to the hotel…

Imagine developers discussing EVERYWHERE in a hotel. Lobby was occupied by few teams, Infra found a table in library corner, Nova took Neutron and occupied breakfast room. Bar area was quite popular and soon some beers were visible here and there. Few teams went to meeting rooms etc. WiFi bandwidth was gone… Some time later hotel staff created a separate wireless network for our use. And then similar situation was on Friday.

On Wednesday other thing happened too: people started receiving information that their flights are cancelled. There were some connections on Thursday and then nothing was flying on Friday. Kudos to hotel staff to be aware of it — they stopped taking external reservations to make sure that PTG attendees have a place to stay for longer (as some people got rebooked to even Thursday).

And even on Saturday it was hard to get to the airport. No taxi going to the hotel due to snow on a street. But if you walked 500 meters then cab could be hailed on a street. Many people went for buses (line 700 was the only working one). The crowd on the airport was huge. Some of those people looked like they lived there (which was probably true). Several flights were delayed (even by 4-5 hours), other got cancelled but most of them were flying.

Despite the weather sitting in a hotel in Dublin was safe, walking around too as there were about 15-20 centimetres of snow on a street. There were several snowmen around, people had fun playing with snow. But at same time local news were informing that 30 000 homes lacked electricity and some people got stuck in their cars. There was no public transport, no trains, no buses. Much smaller amount of people on streets.

Was it worth attending? Yes. Will I attend next ones? Probably not as this is very developer related where I spend most of my OpenStack time around building it’s components or doing some testing.

OpenStack community released ‘queens’ version this week. IMHO it is quite important moment for AArch64 community as well because it works out of the box for us.

Gone are things like setting hw_firmware_type=uefi for each image you upload to Glance — Nova assumes UEFI to be the default firmware on AArch64 (unless you set the variable to different value for some reason). This simplifies things as users does not have to worry about and we should have less support questions on new setups of Linaro Developer Cloud (which will be based on ‘Queens’ instead of ‘Newton’).

There is a working graphical console if your guest image uses properly configured kernel (4.14 from Debian/stretch-backports works fine, 4.4 from Ubuntu/xenial (used by CirrOS) does not have graphics enabled). Handy feature which we were asked already by some users.

Sad thing is state of live migration on AArch64. It simply does not work through the whole stack (Nova, libvirt, QEMU) because we have no idea what exactly cpu we are running on and how it is compatible with other cpu cores. In theory live migration between same type of processors (like XGene1 -> XGene1) should be possible but we do not have even that level of information available. More information can be found in bug 1430987 reported against libvirt.

Less sad part? We set cpu_model to ‘host-passthrough’ by default now (in Nova) so nevermind which deployment method is used it should work out of the box.

When it comes to building (Kolla) and deploying (Kolla Ansible) most of the changes were done during Pike cycle. During Queens’ one most of the changes were small tweaks here and there. I think that our biggest change was convincing everyone in Kolla(-ansible) to migrate from MariaDB 10.0.x (usually from external repositories) to 10.1.x taken from distribution (Debian) or from RDO.

What will Rocky bring? Better hotplug for PCI Express machines (AArch64/virt, x86/q35 models) is one thing. I hope that live migration stuff situation will improve as well.

You run VM instance. Never mind is it part of OpenStack setup or just local one started using Boxes, virt-manager, virsh or other that kind of fronted to libvirt daemon.

Let hotplug some hardware

Then you want to add some virtual hardware to it. And another card and one more controller…

Easy to imagine scenario, right? What can go wrong, you say? “No more available PCI slots.” message can happen. On second/third card or controller… But how? Why?

Like I wrote in one of my previous posts most of VM instances are 90s pc hardware virtual boxes. With simple PCI bus which accepts several cards to be added/removed at any moment.

PCI Express is different

Things are different on AArch64 architecture. Or on x86-64 with Q35 machine type. What is a difference? Both are PCI Express machines. And by default they have far too small amount of pcie slots (called pcie-root-port in qemu/libvirt language). More about PCI Express support can be found in PCI topology and hotplug page of libvirt documentation.

So I wrote a patch to Nova to make sure that enough slots will be available. And then started testing. Tried few different approaches, discussed with upstream libvirt developers about ways of solving the problem and finally we selected the one and only proper way of doing it. Then discussed failures with UEFI developers. And went for help to Qemu authors. And explained what I want to achieve and why to everyone in each of those four projects. At some point I had seen pcie-root-port things everywhere…

Turned out that the method of fixing it is kind of simple: we have to create whole pcie structure with root port and slots. This tells libvirt to not try any automatic adding of slots (which may be tricky if not configured properly as you may end with too small amount of slots for basic addons).

More PCI Express slots

Then I went with idea of using insane values. VM with one hundred PCIe slots? Sure. So I made one, booted it and then something weird happen: landed in UEFI shell instead of getting system booted. Why? How? Where is my storage? Network? Etc?

Limits, limits everywhere…

Turns out that Qemu has limits. And libvirt has limits… All ports/slots went into one bus and memory for MMCONFIG and/or I/O space was gone. There are two interesting threads about it on qemu-devel mailing list.

So I added magic number into my patch: 28 — this amount of pcie-root-port entries in my aarch64 VM instance was giving me bootable system. Have to check it on x86-64/q35 setup still but it should be more or less the same. I expect this patch to land in ‘Rocky’ (the next OpenStack release) and probably will have to find a way to get it into ‘Queens’ as well because this is what we are planning to use for next edition of Linaro Developer Cloud.

Conclusion

Hotplug may be complicated. But issues with it can be solved.

There are so many musical bands and signers that not every one can get popular. Sometimes they are popular in their country/region but not necessary worldwide. Or they get one good song and nothing else gets such popularity. So called ‘one hit wonders’.

One of my friends recently shared “one hit wonders” playlist. But as it is with all those lists created during parties it contained several false entries which rather shown that someone did not know other hits for some bands. Anyway it was interesting enough to play in background.

Music was playing, letters were scrolling in terminal so I took a bit of time and created something more fancy: playlist with less known hits of ‘one-hit wonders’.

Sure, there are many missing entries and that some of listed artists/bands were more popular here and there. I am open for suggestions ;D

People write blogs. People read blogs. But sometimes it is hard to find blogs of all those interesting people. That’s where so called “planets” are solution.

Years ago there was “Planet Linaro” website filled with blog posts from Linaro developers. Then it vanished. Later it got replaced by poor substitute.

But I do not want to have to track each Linaro developer to find their blog and add it into Feedly. So instead I decided to create new planet website. And that’s how Developers Planet got born.

So far it lists a bunch of blogs of Linaro developers. I used venus to run it. Few years old code but runs. Will adapt HTML/CSS template to be a bit more modern.

And why .cf domain? It is free — that’s why.

OpenStack users are used to have graphical console available. They take it for granted even. But we lacked it…

We want graphics on AArch64

When we started working on OpenStack on 64-bit ARM there were many things missing. Most of them got sorted out already. One thing was still in a queue: graphical console. So two weeks ago I started looking at the issue.

Whenever someone tried to use it Nova reported one simple message: “No free USB ports.” You can ask what it has to console? I thought similar and started digging…

Long live architecture differences

As usual reason was simple: yet another aarch64 <> x86 difference in libvirt. Turned out that arm64 is one of those few architectures which do not have USB host controller in default setup. When Nova is told to provide graphical console it adds Spice (or VNC) graphics, video card and USB tablet. But in our case VM instance does not have any USB ports so VM start fails with “No free USB ports” message.

Let patch Nova

Solution was simple: let’s add USB host controller into VM instance. But where? Should libvirt do that or should Nova? I discussed it with libvirt developers and got mixed answers. Opened a bug for it and went to Nova hacking.

Turned out that Nova code for building guest configuration is not that complicated. I created a patch to add USB host controller and waited for code reviews. There were many suggestions, opinions and questions. So I rewrote code. And then again. And again. Finally 15th version got “looks good” opinion from all reviewers and got merged.

Final effect

And how result looks? Boring as it should:

Do you know what is the most popular PC machine nowadays? It is “simple” PCI based x86(-64) machine with i440fx chipset and some expansion cards. Everyone is using them daily. Often you do not even realise that things you do online are handled by machines from 90s.

What? 90s hardware in modern world?

Sounds like a heresy? Who would use 90s hardware in modern world? PCI cards were supposed to be replaced by PCI Express etc, right? No one uses USB 1.x host controllers, hard to find PS/2 mouse or keyboard in stores etc. And you all are wrong…

Meet virtual PC

Most of virtual machines in x86 world is a weird mix of 90s hardware with a bunch of PCI cards to keep them usable in modern world. Parallel ATA storage went to trash replaced by SCSI/SATA/virtual ones. Graphic card is usually simple framebuffer without any 3D acceleration (so like 90s) and typical PS/2 input devices connected. And you have USB 1.1 and 2.0 controllers with one tablet connected. Sounds like retro machines my friends prepare for retro events.

You can upgrade to USB 3.0 controller, graphic card with some 3D acceleration. Or add more memory and cpu cores that i440fx based PC owner ever dreamt about. But it is still 90s hardware.

What about some XXI century hardware?

Want to have something more modern? You can migrate to PCI Express. But nearly no one does that in virtual x86 world. And in AArch64 world we start from here.

And that’s the reason why working with developers of projects related to virtualization (qemu, libvirt, openstack) can be frustrating.

Issues with hotplug?

Hotplug issues? Which hotplug issues? My VM instance allows to plug 10 cards while it is running so where is a problem? The problem is that your machine is 90s hardware with simple PCI bus and 31 slots present on virtual mainboard while VM instance with PCI Express (aarch64, x86 with q35 model) has only TWO free slots present on motherboard. And once they are used no new slots arrive. Unless you shutdown, add free slots and power up again.

Architecture differences?

Or my recent stuff: adding USB host controller. x86 has it because someone ‘made a mistake’ in past and enabled it. But other architectures got sorted out and did not get it. Now all of them need to have it added when it is needed. Have a patch to Nova for it and I am rewriting it again and again to get it into acceptable form.

Partitioning is fun too. There are so many people who fear switching to GPT…

What connects those names? All of them are conference or team meeting names. Spread over Europe + Asia. And I will be on all of them this year.

First will be in Brno, Czechia. Terrible city to travel to but amount of people I can meet there is enormous. Some guys from my Red Hat team will be there, my boss’ boss (and boss of my boss’ boss) and several people from CentOS, Fedora, RHEL (and some other names) communities. Meetings, sessions… Nice to be there. Will be in A-Sport hotel as it is closest to Red Hat office where I have some meetings to attend.

Then FOSDEM. The only “week-long conference squeezed into two days” I know. Good luck with meeting me probably. As usual my list of sessions covers all buildings and have several conflicts. Will meet many people, miss even more, do some beers. This year I stay in Floris Arlequin Grand-Place hotel.

Next one? OpenStack PTG in Dublin, Ireland. Finally will meet all those developers reviewing my patches, helping me with understanding source code of several OpenStack projects. And probably answering several questions about state of AArch64 support. Conference hotel.

Linaro Connect. Hong Kong again. Not registered yet, not looked at flights. Have to do that sooner than later and checking which airline sucks less on intercontinental connections sucks too. With few members of SDI team I will talk about our journey through/with OpenStack on our beloved architecture. Conference hotel.

What after those? Probably OpenSource Day in Poland, maybe some other ones. Will see.