Messages in this thread | | | Date | Wed, 27 Mar 2024 19:12:06 +0000 | Subject | Re: [PATCH v1 0/3] Speed up boot with faster linear map creation | From | Ryan Roberts <> |
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On 26/03/2024 10:14, Ryan Roberts wrote: > Hi All, > > It turns out that creating the linear map can take a significant proportion of > the total boot time, especially when rodata=full. And a large portion of the > time it takes to create the linear map is issuing TLBIs. This series reworks the > kernel pgtable generation code to significantly reduce the number of TLBIs. See > each patch for details. > > The below shows the execution time of map_mem() across a couple of different > systems with different RAM configurations. We measure after applying each patch > and show the improvement relative to base (v6.9-rc1): > > | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra > | VM, 16G | VM, 64G | VM, 256G | Metal, 512G > ---------------|-------------|-------------|-------------|------------- > | ms (%) | ms (%) | ms (%) | ms (%) > ---------------|-------------|-------------|-------------|------------- > base | 151 (0%) | 2191 (0%) | 8990 (0%) | 17443 (0%) > no-cont-remap | 77 (-49%) | 429 (-80%) | 1753 (-80%) | 3796 (-78%) > no-alloc-remap | 77 (-49%) | 375 (-83%) | 1532 (-83%) | 3366 (-81%) > lazy-unmap | 63 (-58%) | 330 (-85%) | 1312 (-85%) | 2929 (-83%)
I've just appended an additional patch to this series. This takes us to a ~95% reduction overall:
| Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra | VM, 16G | VM, 64G | VM, 256G | Metal, 512G ---------------|-------------|-------------|-------------|------------- | ms (%) | ms (%) | ms (%) | ms (%) ---------------|-------------|-------------|-------------|------------- base | 151 (0%) | 2191 (0%) | 8990 (0%) | 17443 (0%) no-cont-remap | 77 (-49%) | 429 (-80%) | 1753 (-80%) | 3796 (-78%) no-alloc-remap | 77 (-49%) | 375 (-83%) | 1532 (-83%) | 3366 (-81%) lazy-unmap | 63 (-58%) | 330 (-85%) | 1312 (-85%) | 2929 (-83%) batch-barriers | 11 (-93%) | 61 (-97%) | 261 (-97%) | 837 (-95%)
Don't believe the intermediate block-based pgtable idea will now be neccessary so I don't intend to persue that. It might be that we choose to drop the middle two patchs; I'm keen to hear opinions.
Thanks, Ryan
> > This series applies on top of v6.9-rc1. All mm selftests pass. I haven't yet > tested all VA size configs (although I don't anticipate any issues); I'll do > this as part of followup. > > Thanks, > Ryan > > > Ryan Roberts (3): > arm64: mm: Don't remap pgtables per- cont(pte|pmd) block > arm64: mm: Don't remap pgtables for allocate vs populate > arm64: mm: Lazily clear pte table mappings from fixmap > > arch/arm64/include/asm/fixmap.h | 5 +- > arch/arm64/include/asm/mmu.h | 8 + > arch/arm64/include/asm/pgtable.h | 4 - > arch/arm64/kernel/cpufeature.c | 10 +- > arch/arm64/mm/fixmap.c | 11 + > arch/arm64/mm/mmu.c | 364 +++++++++++++++++++++++-------- > include/linux/pgtable.h | 8 + > 7 files changed, 307 insertions(+), 103 deletions(-) > > -- > 2.25.1 >
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