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

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Date:   Fri, 9 Nov 2018 13:44:09 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.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 02:37:03PM -0500, Steven Rostedt wrote:
> On Fri, 9 Nov 2018 11:05:51 -0800
> Andy Lutomirski <luto@...capital.net> wrote:
> 
> > > 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.
> > > 
> > >   
> > 
> > Indeed.
> > 
> > Although I had assumed that tracepoints already had appropriate jump label magic.
> 
> It does. But that's not the problem I was trying to solve. It's that
> tracing took a 8% noise dive with retpolines when enabled (hackbench
> slowed down by 8% with all the trace events enabled compared to all
> trace events enabled without retpoline). That is, normal users (those
> not tracinng) are not affected by trace events slowing down by
> retpoline. Those that care about performance when they are tracing, are
> affected by retpoline, quite drastically.
> 
> I'm doing another test run and measurements, to see how the unoptimized
> trampolines help, followed by the trampoline case.

Are you sure you're using unoptimized?  Optimized is the default on
x86-64 (with my third patch).

-- 
Josh