linux-kernel - Re: [PATCH RFC 0/3] Static calls

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Message-ID: <20181109164137.5cngbfrkm4ihj4ra@treble>
Date:   Fri, 9 Nov 2018 10:41:37 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>,
        David Laight <David.Laight@...lab.com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH RFC 0/3] Static calls

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:
> > On Thu, Nov 8, 2018 at 11:28 PM Ingo Molnar <mingo@...nel.org> wrote:
> > >
> > >
> > > 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.
> > 
> > For tracing, we'd want static_call_set_to_nop() or something like that, right?
> 
> Are we talking about tracepoints?  Or ftrace?

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.

-- 
Josh