linux-kernel - Re: [PATCH v2 0/4] Static calls

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Date:   Mon, 26 Nov 2018 16:24:20 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.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>,
        Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 0/4] Static calls

On Mon, Nov 26, 2018 at 03:54:05PM -0500, Steven Rostedt wrote:
> In summary, we had this:
> 
> No RETPOLINES:
>             1.4503 +- 0.0148 seconds time elapsed  ( +-  1.02% )
> 
> baseline RETPOLINES:
>             1.5120 +- 0.0133 seconds time elapsed  ( +-  0.88% )
> 
> Added direct calls for trace_events:
>             1.5239 +- 0.0139 seconds time elapsed  ( +-  0.91% )
> 
> With static calls:
>             1.5282 +- 0.0135 seconds time elapsed  ( +-  0.88% )
> 
> With static call trampolines:
>            1.48328 +- 0.00515 seconds time elapsed  ( +-  0.35% )
> 
> Full static calls:
>            1.47364 +- 0.00706 seconds time elapsed  ( +-  0.48% )
> 
> 
> Adding Retpolines caused a 1.5120 / 1.4503 = 1.0425 ( 4.25% ) slowdown
> 
> Trampolines made it into 1.48328 / 1.4503 = 1.0227 ( 2.27% ) slowdown
> 
> With full static calls 1.47364 / 1.4503 = 1.0160 ( 1.6% ) slowdown
> 
> Going from 4.25 to 1.6 isn't bad, and I think this is very much worth
> the effort. I did not expect it to go to 0% as there's a lot of other
> places that retpolines cause issues, but this shows that it does help
> the tracing code.
> 
> I originally did the tests with the development config, which has a
> bunch of debugging options enabled (hackbench usually takes over 9
> seconds, not the 1.5 that was done here), and the slowdown was closer
> to 9% with retpolines. If people want me to do this with that, or I can
> send them the config. Or better yet, the code is here, just use your
> own configs.

Thanks a lot for running these.  This looks like a nice speedup.  Also a
nice reduction in the standard deviation.

Should I add your tracepoint patch to the next version of my patches?

-- 
Josh