From: Mark Rutland <mark.rutland@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Huang Shijie <shijie@os.amperecomputing.com>,
catalin.marinas@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 11:40:09 +0000 [thread overview]
Message-ID: <ZV3omRGtVS9l-tKk@FVFF77S0Q05N> (raw)
In-Reply-To: <20231122094857.GA2959@willie-the-truck>
On Wed, Nov 22, 2023 at 09:48:57AM +0000, Will Deacon wrote:
> 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.
I agree, and I'd also like to drop ARM64_HAS_NO_HW_PREFETCH.
Mark.
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next prev parent reply other threads:[~2023-11-22 11:40 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 ` [PATCH 0/4] arm64: an optimization " Will Deacon
2023-11-22 11:40 ` Mark Rutland [this message]
2023-11-22 12:11 ` Marc Zyngier
2023-11-23 7:59 ` Linus Walleij
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