linux-kernel - Re: [PATCH v3 0/3] Speed up boot with faster linear map creation

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Message-ID: <ZhlLiM912mFj_dam@FVFF77S0Q05N.cambridge.arm.com>
Date: Fri, 12 Apr 2024 15:56:08 +0100
From: Mark Rutland <mark.rutland@....com>
To: Ryan Roberts <ryan.roberts@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Cc: 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 v3 0/3] Speed up boot with faster linear map creation

On Fri, Apr 12, 2024 at 02:19:05PM +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           |  168   (0%) | 2198   (0%) | 8644   (0%) | 17447   (0%)
> no-cont-remap  |   78 (-53%) |  435 (-80%) | 1723 (-80%) |  3779 (-78%)
> batch-barriers |   11 (-93%) |  161 (-93%) |  656 (-92%) |  1654 (-91%)
> no-alloc-remap |   10 (-94%) |  104 (-95%) |  438 (-95%) |  1223 (-93%)
> 
> 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.

Nice!

> Ryan Roberts (3):
>   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

For the series:

Reviewed-by: Mark Rutland <mark.rutland@....com>

Catalin, Will, are you happy to pick this up?

Mark.