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Thu, 17 Oct 2024 14:08:25 +0200 Message-ID: <9f3f6bd9-47d1-45fa-aa6b-9e0a80a5ebc6@gmx.de> Date: Thu, 17 Oct 2024 14:08:19 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 14/16] modules: Support extended MODVERSIONS info To: Luis Chamberlain , Matthew Maurer , Lucas De Marchi , Petr Pavlu , Sami Tolvanen , Daniel Gomez Cc: masahiroy@kernel.org, ndesaulniers@google.com, ojeda@kernel.org, gary@garyguo.net, Michael Ellerman , Alex Gaynor , Benjamin Gray , Naveen N Rao , rust-for-linux@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, neal@gompa.dev, marcan@marcan.st, j@jannau.net, asahi@lists.linux.dev, linux-modules@vger.kernel.org, Nicholas Piggin , Christophe Leroy , Madhavan Srinivasan , Boqun Feng , =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , linuxppc-dev@lists.ozlabs.org References: <20240925233854.90072-1-mmaurer@google.com> <20240925233854.90072-15-mmaurer@google.com> Content-Language: en-US From: Helge Deller Autocrypt: addr=deller@gmx.de; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:1p/e1F7ttuQMGYqopn2AVUGUZu0cSHvDj1je+893fZhbGOowbgG 5i2/oeoXvkVZFcqxeeGVcshUV+bPEyKpwh/R6+lxFTVQes/H2q6d24GRNoUfC/qEWdq5AmX Y+VU1Qomtnmmtoi7cDYJKzqkC/+JaZaDZ6mcWbB1B4Vf7/vsZfnrBL0/fWx8fbpCjz5OYfE BWGNMEPcCvO/TVqU6Q1PA== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:WsAm6YIyu1Y=;TVmdySOtqVVUrEvY6gGeOBWy5Zv 55RIC3BP1W2gS4gwBWDOK8xth0SuXrw9Uar0o92Dq+5eHtWhGn1HR+QFA8x/uN67qj9Re9HLv Q19ks49VUOMD5Em4MqbiPVDpnn+anlED9LEU2LP+x5plzDKtP5I5A23H5wHZHBrdDH1xpG9mn EMngh5UUDO3EHodIT+u8oNj15qECfhTVqLF4Jj2rjpCaR8IofLuRbXF0RVhVgoA60Di/oMM9x Ag344rqbGSNRQu29oZTT3xS/KaiFiybZXyrFfPoZ4/EDs5vdK2+8SZ1g8zmqH+6+jlqQYBsWp KvW6iZ+uNVr7AlOvGMvFG6SPXL4fZVdHfUwF5vmfMFwbvLVPYmx1nJ7pw4NpVuymOpT+THjLS BPw5U3UTv8AlCuaMl2XaVtENIapcW2lyFHLr9Btc8XEdhDUpff0dLEicdeHsdxepuvgww2Qco FVAiefJsW3lQo7nNZMyVjiLHbTtbpVV3CkbzxlcqwAQjR9wBR6AtCUq2XoCBD7I5d5/WMFDbr JUPLaUjrLsFEvX8u6+RNTtI8OcUJPS6mpuTeGtN4NCv2VlyJqqn+WykH2h35Vk5tOTn2Qwdov iP1Ln8WR6asIZq1Kki6mLimqId3av5Q61R0IRoHBO2+yaESS3TkyRTiR0LF2z0CuD+yhi2kkG mri5zTQNT2NzUeNzZzmcleV9GaFRjdmBWOg9PEbuHA5h50m4kHBHN4A8CeBuBtShtzWU1TMMg GHz8KTEq5eXzWgfek79kXFnZLa9LhphcXG2sq/eMj0kDg7IUnsy/0c5LO+5qTYIs69JhAEr9u qmbQ4fqYyIFEbjMUF6zVjV6+ybV623Tvj6Q8fo751+YdU= 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=3D20241016-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 un= alignment 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/tr= ee/Documentation/core-api/unaligned-memory-access.rst