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Date:   Fri, 9 Nov 2018 13:42:41 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     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>
Subject: Re: [PATCH RFC 0/3] Static calls
Message-ID: <20181109134241.5f4ce3be@gandalf.local.home>
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On Fri, 9 Nov 2018 10:41:37 -0600
Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> 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@kernel.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.
> 

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.

-- Steve