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References: <20240412131908.433043-1-ryan.roberts@arm.com>
In-Reply-To: <20240412131908.433043-1-ryan.roberts@arm.com>
From: Ard Biesheuvel <ardb@kernel.org>
Date: Fri, 12 Apr 2024 17:00:41 +0200
Message-ID: <CAMj1kXEo_t4hgm=jax-0soCCoq6ev-FqMMjU5iXqn06mpUH6+g@mail.gmail.com>
Subject: Re: [PATCH v3 0/3] Speed up boot with faster linear map creation
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, 
	Mark Rutland <mark.rutland@arm.com>, David Hildenbrand <david@redhat.com>, 
	Donald Dutile <ddutile@redhat.com>, Eric Chanudet <echanude@redhat.com>, 
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"

On Fri, 12 Apr 2024 at 15:19, Ryan Roberts <ryan.roberts@arm.com> 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.
..
>
> 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: Ard Biesheuvel <ardb@kernel.org>