On Mon, Jun 22, 2020 at 06:18:02PM -0700, Saravana Kannan wrote: > 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 > > Cc: Ard Biesheuvel <[email protected]> > Signed-off-by: Saravana Kannan <[email protected]> > --- > > v1 -> v2: > - Provided more details in the commit text > - Pulled in Will's comments on the coding style > - Pulled in Ard's suggestion about skipping jumps with the same section > index (parts of Will's suggested code) > > arch/arm64/kernel/module-plts.c | 46 ++++++++++++++++++++++++++++++--- > 1 file changed, 43 insertions(+), 3 deletions(-)
Nice, it looks like you were more-or-less able to use my suggestion directly! Commit message looks much better to, so: Acked-by: Will Deacon <[email protected]> Catalin can pick this up when he starts queuing patches for 5.9. Cheers, Will
