From: Will Deacon <will@kernel.org>
To: Yury Norov <yury.norov@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, Alexey Klimov <aklimov@redhat.com>
Subject: Re: [PATCH] arm64: enable GENERIC_FIND_FIRST_BIT
Date: Wed, 24 Feb 2021 09:33:44 +0000 [thread overview]
Message-ID: <20210224093343.GA11306@willie-the-truck> (raw)
In-Reply-To: <20210224052744.GA1168363@yury-ThinkPad>
On Tue, Feb 23, 2021 at 09:27:44PM -0800, Yury Norov wrote:
> On Tue, Dec 08, 2020 at 10:35:50AM +0000, Will Deacon wrote:
> > On Mon, Dec 07, 2020 at 05:59:16PM -0800, Yury Norov wrote:
> > > (CC: Alexey Klimov)
> > >
> > > On Mon, Dec 7, 2020 at 3:25 AM Will Deacon <will@kernel.org> wrote:
> > > >
> > > > On Sat, Dec 05, 2020 at 08:54:06AM -0800, Yury Norov wrote:
> > > > > ARM64 doesn't implement find_first_{zero}_bit in arch code and doesn't
> > > > > enable it in config. It leads to using find_next_bit() which is less
> > > > > efficient:
> > > >
> > > > [...]
> > > >
> > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > > > > index 1515f6f153a0..2b90ef1f548e 100644
> > > > > --- a/arch/arm64/Kconfig
> > > > > +++ b/arch/arm64/Kconfig
> > > > > @@ -106,6 +106,7 @@ config ARM64
> > > > > select GENERIC_CPU_AUTOPROBE
> > > > > select GENERIC_CPU_VULNERABILITIES
> > > > > select GENERIC_EARLY_IOREMAP
> > > > > + select GENERIC_FIND_FIRST_BIT
> > > >
> > > > Does this actually make any measurable difference? The disassembly with
> > > > or without this is _very_ similar for me (clang 11).
> > > >
> > > > Will
> > >
> > > On A-53 find_first_bit() is almost twice faster than find_next_bit(),
> > > according to
> > > lib/find_bit_benchmark. (Thanks to Alexey for testing.)
> >
> > I guess it's more compiler dependent than anything else, and it's a pity
> > that find_next_bit() isn't implemented in terms of the generic
> > find_first_bit() tbh, but if the numbers are as you suggest then I don't
> > have a problem selecting this on arm64.
>
> Ping?
Not sure what happened to this. Maybe resend at -rc1?
Will
next prev parent reply other threads:[~2021-02-24 9:35 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-05 16:54 [PATCH] arm64: enable GENERIC_FIND_FIRST_BIT Yury Norov
2020-12-07 11:25 ` Will Deacon
2020-12-08 1:59 ` Yury Norov
2020-12-08 10:35 ` Will Deacon
2021-02-24 5:27 ` Yury Norov
2021-02-24 9:33 ` Will Deacon [this message]
2021-02-24 11:52 ` Alexander Lobakin
2021-02-24 15:44 ` Yury Norov
2021-02-25 11:53 ` Alexander Lobakin
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=20210224093343.GA11306@willie-the-truck \
--to=will@kernel.org \
--cc=aklimov@redhat.com \
--cc=catalin.marinas@arm.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=yury.norov@gmail.com \
/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).