From: Ingo Molnar <mingo@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Andy Lutomirski <luto@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
David Laight <David.Laight@ACULAB.COM>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH RFC 0/3] Static calls
Date: Fri, 9 Nov 2018 08:28:11 +0100 [thread overview]
Message-ID: <20181109072811.GB86700@gmail.com> (raw)
In-Reply-To: <cover.1541711457.git.jpoimboe@redhat.com>
* Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> These patches are related to two similar patch sets from Ard and Steve:
>
> - https://lkml.kernel.org/r/20181005081333.15018-1-ard.biesheuvel@linaro.org
> - https://lkml.kernel.org/r/20181006015110.653946300@goodmis.org
>
> The code is also heavily inspired by the jump label code, as some of the
> concepts are very similar.
>
> There are three separate implementations, depending on what the arch
> supports:
>
> 1) CONFIG_HAVE_STATIC_CALL_OPTIMIZED: patched call sites - requires
> objtool and a small amount of arch code
>
> 2) CONFIG_HAVE_STATIC_CALL_UNOPTIMIZED: patched trampolines - requires
> a small amount of arch code
>
> 3) If no arch support, fall back to regular function pointers
>
>
> TODO:
>
> - I'm not sure about the objtool approach. Objtool is (currently)
> x86-64 only, which means we have to use the "unoptimized" version
> everywhere else. I may experiment with a GCC plugin instead.
I'd prefer the objtool approach. It's a pretty reliable first-principles
approach while GCC plugin would have to be replicated for Clang and any
other compilers, etc.
> - Does this feature have much value without retpolines? If not, should
> we make it depend on retpolines somehow?
Paravirt patching, as you mention in your later reply?
> - Find some actual users of the interfaces (tracepoints? crypto?)
I'd be very happy with a demonstrated paravirt optimization already -
i.e. seeing the before/after effect on the vmlinux with an x86 distro
config.
All major Linux distributions enable CONFIG_PARAVIRT=y and
CONFIG_PARAVIRT_XXL=y on x86 at the moment, so optimizing it away as much
as possible in the 99.999% cases where it's not used is a primary
concern.
All other usecases are bonus, but it would certainly be interesting to
investigate the impact of using these APIs for tracing: that too is a
feature enabled everywhere but utilized only by a small fraction of Linux
users - so literally every single cycle or instruction saved or hot-path
shortened is a major win.
Thanks,
Ingo
next prev parent reply other threads:[~2018-11-09 7:28 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-08 21:15 [PATCH RFC 0/3] Static calls Josh Poimboeuf
2018-11-08 21:15 ` [RFC PATCH 1/3] static_call: Add static call infrastructure Josh Poimboeuf
2018-11-09 9:51 ` Ard Biesheuvel
2018-11-09 14:55 ` Josh Poimboeuf
2018-11-09 13:39 ` Ard Biesheuvel
2018-11-09 15:10 ` Josh Poimboeuf
2018-11-09 15:14 ` Ard Biesheuvel
2018-11-09 17:25 ` Ard Biesheuvel
2018-11-09 17:31 ` Josh Poimboeuf
2018-11-09 17:33 ` Ard Biesheuvel
2018-11-09 17:46 ` Josh Poimboeuf
2018-11-09 17:52 ` Ard Biesheuvel
2018-11-09 17:53 ` Ard Biesheuvel
2018-11-09 19:03 ` Josh Poimboeuf
2018-11-09 19:12 ` Ard Biesheuvel
2018-11-09 17:33 ` Josh Poimboeuf
2018-11-09 18:33 ` Steven Rostedt
2018-11-09 19:35 ` Josh Poimboeuf
2018-11-09 19:57 ` Steven Rostedt
2018-11-09 20:34 ` Josh Poimboeuf
2018-11-10 5:10 ` Steven Rostedt
2018-11-10 11:58 ` Ard Biesheuvel
2018-11-10 13:09 ` Steven Rostedt
2018-11-12 3:07 ` Josh Poimboeuf
2018-11-12 4:39 ` Ard Biesheuvel
2018-11-12 4:56 ` Josh Poimboeuf
2018-11-12 5:02 ` Ard Biesheuvel
2018-11-10 11:56 ` Ard Biesheuvel
2018-11-08 21:15 ` [RFC PATCH 2/3] x86/static_call: Add x86 unoptimized static call implementation Josh Poimboeuf
2018-11-08 21:15 ` [RFC PATCH 3/3] x86/static_call: Add optimized static call implementation for 64-bit Josh Poimboeuf
2018-11-08 21:24 ` [PATCH RFC 0/3] Static calls Josh Poimboeuf
2018-11-09 7:28 ` Ingo Molnar [this message]
2018-11-09 7:50 ` Ingo Molnar
2018-11-09 13:50 ` Ard Biesheuvel
2018-11-09 15:20 ` Josh Poimboeuf
2018-11-10 23:20 ` Peter Zijlstra
2018-11-11 13:42 ` Ard Biesheuvel
2018-11-11 14:25 ` Peter Zijlstra
2018-11-09 14:45 ` Josh Poimboeuf
2018-11-12 5:02 ` Ingo Molnar
2018-11-12 5:30 ` Josh Poimboeuf
2018-11-12 9:39 ` Ard Biesheuvel
2018-11-12 22:52 ` Josh Poimboeuf
2018-11-12 17:03 ` Steven Rostedt
2018-11-12 22:56 ` Josh Poimboeuf
2018-11-12 5:34 ` Andy Lutomirski
2018-11-09 15:16 ` Andy Lutomirski
2018-11-09 15:21 ` Josh Poimboeuf
2018-11-09 16:41 ` Josh Poimboeuf
2018-11-09 18:42 ` Steven Rostedt
2018-11-09 19:05 ` Andy Lutomirski
2018-11-09 19:37 ` Steven Rostedt
2018-11-09 19:44 ` Josh Poimboeuf
2018-11-09 19:59 ` Steven Rostedt
2018-11-09 20:36 ` Josh Poimboeuf
2018-11-10 15:13 ` Masami Hiramatsu
2018-11-09 20:53 ` Rasmus Villemoes
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