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Subject: Re: [PATCH RFC 0/3] Static calls
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <20181109134241.5f4ce3be@gandalf.local.home>
Date:   Fri, 9 Nov 2018 11:05:51 -0800
Cc:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.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>
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Message-Id: <979DB163-EFBD-41BB-8481-155AAF526E72@amacapital.net>
References: <cover.1541711457.git.jpoimboe@redhat.com> <20181109072811.GB86700@gmail.com> <CALCETrU3tPPOiuTaLqUy-L4sPvZRU8BLYML-BgQH_LZhA4bzSQ@mail.gmail.com> <20181109152139.zig45f6gp24btfbc@treble> <20181109164137.5cngbfrkm4ihj4ra@treble> <20181109134241.5f4ce3be@gandalf.local.home>
To:     Steven Rostedt <rostedt@goodmis.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On Nov 9, 2018, at 10:42 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
>=20
> On Fri, 9 Nov 2018 10:41:37 -0600
> Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>=20
>>> On Fri, Nov 09, 2018 at 09:21:39AM -0600, Josh Poimboeuf wrote:
>>>> On Fri, Nov 09, 2018 at 07:16:17AM -0800, Andy Lutomirski wrote: =20
>>>>> On Thu, Nov 8, 2018 at 11:28 PM Ingo Molnar <mingo@kernel.org> wrote: =
=20
>>>>>=20
>>>>>=20
>>>>> 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 Li=
nux
>>>>> users - so literally every single cycle or instruction saved or hot-pa=
th
>>>>> shortened is a major win. =20
>>>>=20
>>>> For tracing, we'd want static_call_set_to_nop() or something like that,=
 right? =20
>>>=20
>>> Are we talking about tracepoints?  Or ftrace? =20
>>=20
>> Since ftrace changes calls to nops, and vice versa, I assume you meant
>> ftrace.  I don't think ftrace is a good candidate for this, as it's
>> inherently more flexible than this API would reasonably allow.
>>=20
>=20
> Not sure what Andy was talking about, but I'm currently implementing
> tracepoints to use this, as tracepoints use indirect calls, and are a
> prime candidate for static calls, as I showed in my original RFC of
> this feature.
>=20
>=20

Indeed.

Although I had assumed that tracepoints already had appropriate jump label m=
agic.=