From: Marc Zyngier <maz@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>,
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,
patches@amperecomputing.com
Subject: Re: [PATCH 0/4] arm64: an optimization for AmpereOne
Date: Wed, 22 Nov 2023 12:11:16 +0000 [thread overview]
Message-ID: <86il5uyom3.wl-maz@kernel.org> (raw)
In-Reply-To: <ZV3omRGtVS9l-tKk@FVFF77S0Q05N>
On Wed, 22 Nov 2023 11:40:09 +0000,
Mark Rutland <mark.rutland@arm.com> wrote:
>
> 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.
+1. Also, as the (most probably) sole user of this remarkable
implementation, I hacked -rc2 to drop ARM64_HAS_NO_HW_PREFETCH. The
result is that a kernel compilation job regressed by 0.4%, something
that I consider being pure noise.
If nobody beats me to it, I'll send the patch.
M.
--
Without deviation from the norm, progress is not possible.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2023-11-22 12:11 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
2023-11-22 12:11 ` Marc Zyngier [this message]
2023-11-23 7:59 ` Linus Walleij
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=86il5uyom3.wl-maz@kernel.org \
--to=maz@kernel.org \
--cc=anshuman.khandual@arm.com \
--cc=broonie@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=oliver.upton@linux.dev \
--cc=patches@amperecomputing.com \
--cc=robh@kernel.org \
--cc=shijie@os.amperecomputing.com \
--cc=suzuki.poulose@arm.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).