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From: Will Deacon <will@kernel.org>
To: Huang Shijie <shijie@os.amperecomputing.com>
Cc: catalin.marinas@arm.com, mark.rutland@arm.com,
	suzuki.poulose@arm.com, broonie@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, anshuman.khandual@arm.com,
	robh@kernel.org, oliver.upton@linux.dev, maz@kernel.org,
	patches@amperecomputing.com
Subject: Re: [PATCH 0/4] arm64: an optimization for AmpereOne
Date: Wed, 22 Nov 2023 09:48:57 +0000	[thread overview]
Message-ID: <20231122094857.GA2959@willie-the-truck> (raw)
In-Reply-To: <20231122092855.4440-1-shijie@os.amperecomputing.com>

On Wed, Nov 22, 2023 at 05:28:51PM +0800, Huang Shijie wrote:
> 0) Background:
>    We found that AmpereOne benefits from aggressive prefetches when
>    using 4K page size.

We tend to shy away from micro-architecture specific optimisations in
the arm64 kernel as they're pretty unmaintainable, hard to test properly,
generally lead to bloat and add additional obstacles to updating our
library routines.

Admittedly, we have something for Thunder-X1 in copy_page() (disguised
as ARM64_HAS_NO_HW_PREFETCH) but, frankly, that machine needed all the
help it could get and given where it is today I suspect we could drop
that code without any material consequences.

So I'd really prefer not to merge this; modern CPUs should do better at
copying data. It's copy_to_user(), not rocket science.

Will

  parent reply	other threads:[~2023-11-22  9:50 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-22  9:28 [PATCH 0/4] arm64: an optimization for AmpereOne Huang Shijie
2023-11-22  9:28 ` [PATCH 1/4] extable: add __sort_main_extable Huang Shijie
2023-11-22  9:28 ` [PATCH 2/4] arm64: alternative: handle the kernel exception table Huang Shijie
2023-11-22  9:28 ` [PATCH 3/4] arm64: copy_template.S: add loop_for_copy_128_bytes macro Huang Shijie
2023-11-22  9:28 ` [PATCH 4/4] arm64: add software prefetches for AmpereOne Huang Shijie
2023-11-22 11:34   ` Robin Murphy
2023-11-22  9:48 ` Will Deacon [this message]
2023-11-22 11:40   ` [PATCH 0/4] arm64: an optimization " Mark Rutland
2023-11-22 12:11     ` Marc Zyngier
2023-11-23  7:59 ` Linus Walleij

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