linux-kernel - Re: [PATCH v2 4/4] arm64: add a new document for the fine-tuning tips

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Message-ID: <e48df345-0946-4b34-a463-e89aa89680f9@arm.com>
Date: Fri, 6 Dec 2024 09:26:32 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Huang Shijie <shijie@...amperecomputing.com>, catalin.marinas@....com,
 will@...nel.org
Cc: patches@...erecomputing.com, paulmck@...nel.org,
 akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
 xiongwei.song@...driver.com, ardb@...nel.org, steven.price@....com,
 suzuki.poulose@....com, mark.rutland@....com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 cl@...amperecomputing.com
Subject: Re: [PATCH v2 4/4] arm64: add a new document for the fine-tuning tips

On 11/26/24 14:26, Huang Shijie wrote:
> Put some fine-tuning tips in this file:
> 	1.) rodata=noalias
> 	2.) slab_strict_numa
> 	3.) CONFIG_SCHED_CLUSTER
> 
> We can add more tips in future.
> 
> Signed-off-by: Huang Shijie <shijie@...amperecomputing.com>
> ---
>  Documentation/arch/arm64/fine-tuning-tips.rst | 23 +++++++++++++++++++
>  Documentation/arch/arm64/index.rst            |  1 +
>  2 files changed, 24 insertions(+)
>  create mode 100644 Documentation/arch/arm64/fine-tuning-tips.rst
> 
> diff --git a/Documentation/arch/arm64/fine-tuning-tips.rst b/Documentation/arch/arm64/fine-tuning-tips.rst
> new file mode 100644
> index 000000000000..70ef1cef92fb
> --- /dev/null
> +++ b/Documentation/arch/arm64/fine-tuning-tips.rst
> @@ -0,0 +1,23 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +================
> +fine-tuning tips
> +================
> +
> +This file contains some fine-tuning tips for arm64 machines.
> +These tips do not gurantee that you can get better performance,
> +but you can try them with your workload.
> +
> +rodata=noalias
> +----------------
> +It can provide us more block mappings and contiguous hits
> +to map the linear region which minimizes the TLB footprint.
> +
> +slab_strict_numa
> +----------------
> +In NUMA, it will provide the local memory allocation by SLUB.
> +
> +CONFIG_SCHED_CLUSTER
> +----------------
> +Some arm64 machines have cpu core cluster, enable it may
> +helps you get better performance.
> diff --git a/Documentation/arch/arm64/index.rst b/Documentation/arch/arm64/index.rst
> index 6a012c98bdcd..36d1ef09bd71 100644
> --- a/Documentation/arch/arm64/index.rst
> +++ b/Documentation/arch/arm64/index.rst
> @@ -16,6 +16,7 @@ ARM64 Architecture
>      cpu-feature-registers
>      cpu-hotplug
>      elf_hwcaps
> +    fine-tuning-tips
>      gcs
>      hugetlbpage
>      kdump
Although the idea for such a file makes sense, to help system admins
tune the kernel command line for required behaviour, I am concerned
about the overall structure and scope for such a document. Should it
contain tips regarding all the subsystems on the platform, till what
extent these details should be described in there and then there are
so many aspects for a required behaviour etc ?

Besides maintaining such a document might also be very difficult as
well given how implementations will change over time thus requiring
different tuning etc. Hence kernel source might not be a place for
such a document.