#9939 ppc64le: changing from 64k to 4k kernel page size
Opened 4 months ago by pocock. Modified 3 months ago

  • Describe the issue

As per the change process, this is a request for Fedora 34 and later to use the 4k page size for the ppc64el architecture. Requires mass rebuild on build servers running with the updated kernel.

  • When do you need this? (YYYY/MM/DD)

Fedora 34

  • When is this no longer needed or useful? (YYYY/MM/DD)

No date known - When all upstreams have supported other page sizes.

  • If we cannot complete your request, what is the impact?

Status quo, difficulty for people who invest in the POWER-based workstations and Blackbird systems from Raptor Computing.


@pocock Do you have a Change proposal page to go with this? (also the arch is ppc64le, not ppc64el)

Out of curiosity, is ppc64el the same as ppc64le?

It is. ppc64el is the Debian name for the ppc64le architecture.

Two names is never enough, the Debian kernel is powerpc64le

$ uname -a
Linux lab1 4.19.0-10-powerpc64le-4k #1 SMP Debian 4.19.132-2 (2020-09-16) ppc64le GNU/Linux

but inside the kernel is ppc64le, like Fedora

$ uname -m
ppc64le

I highly recommend using the term ppc64le in the proposal before it is announced, to avoid more confusion. ppc64le is the name used in Fedora.

I've gone ahead and just made the edit to switch the arch name reference. @pocock, please consistently use the architecture name ppc64le when communicating about it to prevent confusion.

Thanks for clarifying, I added it to the f34 mass rebuild tasks.

Metadata Update from @mohanboddu:
- Issue tagged with: change-ack, changes, f34, mass rebuild, medium-gain, medium-trouble, ops

4 months ago

So, this change is something that would be changed in the kernel package right?

You say "Requires mass rebuild on build servers running with the updated kernel." do we really need to be running a kernel with 4k pages for the mass rebuild? ie, are there things that take the pagesize from the running kernel only? Or is it enough to just make this change in the built kernel package?

It may be logistically anoying to do this, but it should be possible (we would need a f33 kernel with 4k pages, and it would prevent us from updating it without doing a custom build).

For the mass-rebuild to be effective, do we need some bootstrap procedure? Like have 4k kernel on the builders first?

So, this change is something that would be changed in the kernel package right?

You say "Requires mass rebuild on build servers running with the updated kernel." do we really need to be running a kernel with 4k pages for the mass rebuild? ie, are there things that take the pagesize from the running kernel only? Or is it enough to just make this change in the built kernel package?

It may be logistically anoying to do this, but it should be possible (we would need a f33 kernel with 4k pages, and it would prevent us from updating it without doing a custom build).

Yes, it is necessary.

A very small number of packages call getconf PAGESIZE or getconf PAGE_SIZE during build and the result of that call impacts the binary that is compiled.

I made some suggestions to detect and correct these builds but that may not be ready for F34 or F35

The changes for mass rebuild were due to be submitted by Dec 29th according to the schedule [1], the mass rebuild is scheduled for next week, it's not really enough time to access the impact and get feedback from all the possibly affected parties.

[1] https://fedorapeople.org/groups/schedule/f-34/f-34-key-tasks.html

@bcotton already wrote to me privately and suggested pushing this back to F35. Personally, I build my own kernels when I need to so that doesn't impact me personally. For new users on F34, I think it is important to consider whether a rushed change to the 4k page size creates more risk than the status quo. It has been raised in various threads on devel over the last 3 months so I don't think it will be a complete surprise to anybody but I don't want to overload people either.

It's been as it it has been ever since the ppc64le bootstrap was done back in Fedora 21 I don't think waiting another cycle to allow better feedback from affected parties to ensure the impact as it is and also to do things like check how many packages are affected by the getconf you mention above

We have some feedback from workstation users, it is very clear, the new GPUs just don't work without this change but they are very happy if they get the 4k page size

We know Vikings is imminently releasing their workstations in Europe, they also developed a custom water-cooling heatsink to make these workstations more attractive than previous generations. These are the people who probably suffer most without making the change in F34.

On the other hand, I agree that existing users may be surprised. Any existing users who monitored the discussions on devel or the Raptor forums would be aware of this possibility. Other users may not be aware of it and haven't provided feedback yet.

Note that a releng ticket is not a best place to discuss this. Could this discussion please be moved to the devel mailing list?

Still discussion is going on, but as per @sharkcz this changed is pushed to F35 for now.

Metadata Update from @mohanboddu:
- Issue untagged with: f34
- Issue tagged with: f35

4 months ago

now that f34 is branched, is it possible to start using the 4k kernel in the build servers or you prefer to wait for later in the release cycle?

now that f34 is branched, is it possible to start using the 4k kernel in the build servers or you prefer to wait for later in the release cycle?

Has the feature been approved for F-35? It needs to be submitted through the process for F-35.

I changed the state in the wiki page to ReadyForWrangler

Do I need to post another update here when it is approved for F-35? Or will somebody do that as part of the change review?

Login to comment on this ticket.

Metadata
Boards 1
Ops Status: Backlog