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d4e0340919
When loading a module, module_frob_arch_sections() tries to figure out the number of PLTs that'll be needed to handle all the RELAs. While doing this, it tries to dedupe PLT allocations for multiple R_AARCH64_CALL26 relocations to the same symbol. It does the same for R_AARCH64_JUMP26 relocations. To make checks for duplicates easier/faster, it sorts the relocation list by type, symbol and addend. That way, to check for a duplicate relocation, it just needs to compare with the previous entry. However, sorting the entire relocation array is unnecessary and expensive (O(n log n)) because there are a lot of other relocation types that don't need deduping or can't be deduped. So this commit partitions the array into entries that need deduping and those that don't. And then sorts just the part that needs deduping. And when CONFIG_RANDOMIZE_BASE is disabled, the sorting is skipped entirely because PLTs are not allocated for R_AARCH64_CALL26 and R_AARCH64_JUMP26 if it's disabled. This gives significant reduction in module load time for modules with large number of relocations with no measurable impact on modules with a small number of relocations. In my test setup with CONFIG_RANDOMIZE_BASE enabled, these were the results for a few downstream modules: Module Size (MB) wlan 14 video codec 3.8 drm 1.8 IPA 2.5 audio 1.2 gpu 1.8 Without this patch: Module Number of entries sorted Module load time (ms) wlan 243739 283 video codec 74029 138 drm 53837 67 IPA 42800 90 audio 21326 27 gpu 20967 32 Total time to load all these module: 637 ms With this patch: Module Number of entries sorted Module load time (ms) wlan 22454 61 video codec 10150 47 drm 13014 40 IPA 8097 63 audio 4606 16 gpu 6527 20 Total time to load all these modules: 247 Time saved during boot for just these 6 modules: 390 ms Signed-off-by: Saravana Kannan <saravanak@google.com> Acked-by: Will Deacon <will@kernel.org> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Link: https://lore.kernel.org/r/20200623011803.91232-1-saravanak@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.