On Thu, Oct 17, 2024 at 02:08:19PM +0200, Helge Deller wrote: > Hi Luis, > > On 10/17/24 01:21, Luis Chamberlain wrote: > > 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
