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SubjectRe: [PATCH v2] arm64/module: Optimize module load time by optimizing PLT counting
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 <ard.biesheuvel@linaro.org>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
>
> 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 <will@kernel.org>

Catalin can pick this up when he starts queuing patches for 5.9.

Cheers,

Will

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