From: Peter Zijlstra <peterz@infradead.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
Quentin Perret <qperret@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
James Morse <james.morse@arm.com>, Will Deacon <will@kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2] arm64: implement support for static call trampolines
Date: Thu, 29 Oct 2020 12:44:57 +0100 [thread overview]
Message-ID: <20201029114457.GL2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAMj1kXHnM-puaCup8+aiPy7ZVCNzUt61M4yVkRi6L5XD47xmwg@mail.gmail.com>
On Thu, Oct 29, 2020 at 12:32:50PM +0100, Ard Biesheuvel wrote:
> However, as I discussed with Will offline yesterday as well, the
> question that got snowed under is whether we need any of this on arm64
> in the first place. It seems highly unlikely that inline static calls
> are worth it, and even out-of-line static calls are probably not worth
> the hassle as we don't have the retpoline problem.
>
> So this code should be considered an invitation for discussion, and
> perhaps someone can invent a use case where benchmarks can show a
> worthwhile improvement. But let's not get ahead of ourselves.
So the obvious benefit is not having to do the extra load. Any indirect
call will have to do a load first, which can miss etc.. And yes,
retpoline is a horrible mess as well.
Doing the direct vs indirect saves one I$ miss I suppose, which can be
noticable.
IIRC Steve had benchmarks for the ftrace conversion, which is now
upstream, so that should be simple enough to run.
Steve, remember how to get numbers out of that?
_______________________________________________
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:[~2020-10-29 11:46 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 18:41 [PATCH v2] arm64: implement support for static call trampolines Ard Biesheuvel
2020-10-29 10:28 ` Peter Zijlstra
2020-10-29 10:40 ` Peter Zijlstra
2020-10-29 10:58 ` Ard Biesheuvel
2020-10-29 11:46 ` Peter Zijlstra
2020-10-29 11:49 ` Ard Biesheuvel
2020-10-29 11:54 ` Peter Zijlstra
2020-10-29 12:14 ` Ard Biesheuvel
2020-10-29 11:27 ` Quentin Perret
2020-10-29 11:32 ` Ard Biesheuvel
2020-10-29 11:44 ` Peter Zijlstra [this message]
2020-10-29 14:10 ` Steven Rostedt
2020-10-29 11:54 ` Quentin Perret
2020-10-29 13:22 ` Ard Biesheuvel
2020-11-16 10:18 ` Quentin Perret
2020-11-16 10:31 ` Ard Biesheuvel
2020-11-16 12:05 ` Quentin Perret
2020-10-29 11:50 ` Mark Rutland
2020-10-29 11:58 ` Peter Zijlstra
2020-10-29 13:30 ` Mark Rutland
2020-10-29 11:59 ` Ard Biesheuvel
2020-10-29 13:21 ` Mark Rutland
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=20201029114457.GL2628@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=ardb@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=james.morse@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=mark.rutland@arm.com \
--cc=qperret@google.com \
--cc=rostedt@goodmis.org \
--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).