linux-kernel - Re: [PATCH v2 0/4] Speed up boot with faster linear map creation

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Date: Fri, 5 Apr 2024 16:39:46 +0900
From: Itaru Kitayama <itaru.kitayama@...ux.dev>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	David Hildenbrand <david@...hat.com>,
	Donald Dutile <ddutile@...hat.com>,
	Eric Chanudet <echanude@...hat.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/4] Speed up boot with faster linear map creation

On Thu, Apr 04, 2024 at 03:33:04PM +0100, 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 most of the time is spent
> waiting on superfluous tlb invalidation and memory barriers. This series reworks
> the kernel pgtable generation code to significantly reduce the number of those
> TLBIs, ISBs and DSBs. 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-rc2):
> 
>                | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra
>                | VM, 16G     | VM, 64G     | VM, 256G    | Metal, 512G
> ---------------|-------------|-------------|-------------|-------------
>                |   ms    (%) |   ms    (%) |   ms    (%) |    ms    (%)
> ---------------|-------------|-------------|-------------|-------------
> base           |  153   (0%) | 2227   (0%) | 8798   (0%) | 17442   (0%)
> no-cont-remap  |   77 (-49%) |  431 (-81%) | 1727 (-80%) |  3796 (-78%)
> batch-barriers |   13 (-92%) |  162 (-93%) |  655 (-93%) |  1656 (-91%)
> no-alloc-remap |   11 (-93%) |  109 (-95%) |  449 (-95%) |  1257 (-93%)
> lazy-unmap     |    6 (-96%) |   61 (-97%) |  257 (-97%) |   838 (-95%)
> 
> This series applies on top of v6.9-rc2. All mm selftests pass. I've compile and
> boot tested various PAGE_SIZE and VA size configs.
> 
> ---
> 
> Changes since v1 [1]
> ====================
> 
>   - Added Tested-by tags (thanks to Eric and Itaru)
>   - Renamed ___set_pte() -> __set_pte_nosync() (per Ard)
>   - Reordered patches (biggest impact & least controversial first)
>   - Reordered alloc/map/unmap functions in mmu.c to aid reader
>   - pte_clear() -> __pte_clear() in clear_fixmap_nosync()
>   - Reverted generic p4d_index() which caused x86 build error. Replaced with
>     unconditional p4d_index() define under arm64.
> 
> 
> [1] https://lore.kernel.org/linux-arm-kernel/20240326101448.3453626-1-ryan.roberts@arm.com/
> 
> Thanks,
> Ryan
> 
> 
> Ryan Roberts (4):
>   arm64: mm: Don't remap pgtables per-cont(pte|pmd) block
>   arm64: mm: Batch dsb and isb when populating pgtables
>   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 |  13 +-
>  arch/arm64/kernel/cpufeature.c   |  10 +-
>  arch/arm64/mm/fixmap.c           |  11 +
>  arch/arm64/mm/mmu.c              | 377 +++++++++++++++++++++++--------
>  6 files changed, 319 insertions(+), 105 deletions(-)
> 
> --
> 2.25.1
>

I've build and boot tested the v2 on FVP, base is taken from your
linux-rr repo. Running run_vmtests.sh on v2 left some gup longterm not oks, would you take a look at it? The mm ksefltests used is from your linux-rr repo too.

Thanks,
Itaru.

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