On Thu, Oct 17, 2024 at 02:08:19PM +0200, Helge Deller wrote:

Hi Luis,

On 10/17/24 01:21, Luis Chamberlain wrote:

quoted

That sounds great. Yeah, the above would be great to test. A while ago
I wrote a new modules selftests in order to test possible improvements
on find_symbol() but I also did this due to push the limits of the
numbers of symbols we could support. I wrote all this to also test the
possible 64-bit alignment benefits of __ksymtab_ sections on
architectures without CONFIG_HAVE_ARCH_PREL32_RELOCATIONS (e.g. ppc64,
ppc64le, parisc, s390x,...). [....]

I forget what we concluded on Helge Deller's alignement patches, I think
there was an idea on how to address the alignment through other means.

[0] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git/log/?h=20241016-modules-symtab

I stumbled upon the unaligned-memory-access.rst document [1].
Please read it, as it is a really good document, and the section
"Why unaligned access is bad" states:
It should be obvious from the above that if your code causes unaligned
memory accesses to happen, your code will not work correctly on certain
platforms and will cause performance problems on others.

With this in mind, you really should apply both of my alignment
patches which you currently carry in [0].

For parisc I partly solved the issue by fixing the arch-specific kernel unalignment
handler, but every time module sections are stored unaligned, it triggers
performance degregation on parisc (and other sensitive platforms).

I suggest you apply them unconditionally.

Helge

[1]  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/core-api/unaligned-memory-access.rst

You're right, I've just referred to that doc and pushed to the new
linux modules [2] modules-next branch. This is also great timing so
that the work that is ongoing for Rust will take this into
consideration as well. I'll just post the test I wrote as separate
thing but it surely can be used to help test some of this later.

[2] git://git.kernel.org/pub/scm/linux/kernel/git/modules/linux.git

  Luis