linux-kernel - Re: [RFC PATCH 00/10] x86: undwarf unwinder

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Message-ID: <3db1be2a-cc33-89f3-950f-cfe1c21ee7f1@suse.cz>
Date:   Thu, 1 Jun 2017 16:08:25 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>
Subject: Re: [RFC PATCH 00/10] x86: undwarf unwinder

Ccing Mel who did proper measurements and can hopefully comment on his
results.

On 06/01/2017, 03:50 PM, Ingo Molnar wrote:
> That's not what I meant! The speedup comes from (hopefully) being able to disable 
> CONFIG_FRAME_POINTER, which:
> 
>  - creates simpler/faster function prologues and epilogues - no managing of RBP 
>    needed
> 
>  - gives one more generic purpose register to work from. This matters less on 
>    64-bit kernels but it's a small effect.
> 
> I've seen numbers of 1-2% of instruction count reduction in common kernel 
> workloads, which would be pretty significant on well cached workloads.

thanks,
-- 
js
suse labs