[SRU][J/K/L:meta-raspi][J/K/L:raspi][PATCH 0/5] raspi-nolpae flavor is pointless nowadays (LP: #2023359)

[Dimitri John Ledkov]

On Tue, 13 Jun 2023 at 09:03, Juerg Haefliger
<juerg.haefliger at canonical.com> wrote:
>
> [Impact]
>
> linux-raspi 5.4 in Focal was the first kernel to support Pi 4B, which requires
> LPAE to be enabled for armhf. Since we currently don't support board-specific
> kernels but follow a one-kernel-fits-all strategy, the LPAE kernel is also used
> on Pi 3 and 2 boards. Back then, running an armhf LPAE kernel on a Pi 3/2
> resulted in additional kernel memory consumption of ~70MB compared to arm64 and
> non-LPAE kernels. For that reason I decided to introduce a raspi-nolpae flavor
> which can be used on Pi 3 and 2 (only). That flavor was never officially
> announced nor installed automatically anywhere. A user has to install it
> manually. We never had any complaints about armhf kernel memory consumption so
> never directed anybody at installing this flavor. Therefore I'm assuming it's
> not being used...
>
> Turns out that the early 5.4 kernels were broken and incorrectly initialized a
> 64MB SWIOTLB buffer which is the reason for the above additional memory
> consumption. This was fixed here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fcf044891c84e38fc90eb736b818781bccf94e38
>
> With this commit, the memory consumption of both the armhf raspi and
> raspi-nolpae flavor are pretty much on par [1] and there is really no reason
> anymore to keep the raspi-nolpae flavor around. So let's get rid of it and
> introduce a transitional package that replaces installed raspi-nolpae packages
> with raspi packages.
>
> [Test Case]
>
> Install raspi-nolpae flavor and upgrade to the new kernel and verify that the
> raspi flavor is installed instead.
>
> [Where Problems Could Occur]
>
> Only users that have the raspi-nolpae flavor installed are affected. Upgrades,
> i.e., transitions from raspi-nolpae to raspi could go wrong. It's not expected
> that there is a user visible difference between running a current raspi-nolpae
> and raspi kernel flavor.
>
> [1]
> arm64 raspi -- Memory: 815528K/970752K available (13376K kernel code, 2472K rwdata, 4296K rodata, 5504K init, 850K bss, 89688K reserved, 65536K cma-reserved)
> armhf raspi -- Memory: 835732K/970752K available (12288K kernel code, 1643K rwdata, 3692K rodata, 2048K init, 533K bss, 69484K reserved, 65536K cma-reserved, 118784K highmem)
> armhf raspi-nolpae -- Memory: 836620K/970752K available (12288K kernel code, 1633K rwdata, 3676K rodata, 1024K init, 511K bss, 68596K reserved, 65536K cma-reserved)
>

Given all of the above, I don't see much point in our
generic/generic-lpae armhf kernel pair either.

If you have time, it would be nice to also prepare patches that make
generic:armhf kernel lpae one, stop building generic-lpae:armhf, make
generic-lpae:armhf a transitional to generic:armhf. If you don't have
time to prepare this let me know, and I'll do a separate submission of
that for mantic onwards.

>
> Patches:
>   1,2: J/K/L linux-meta-raspi
>   3:   J linux-raspi
>   4:   K linux-raspi
>   5:   L linux-raspi
>
> --
> 2.37.2
>
> --
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team



-- 
okurrr,

Dimitri