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

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Message-ID: <20170601132523.quyvnej54y23hel4@hirez.programming.kicks-ass.net>
Date:   Thu, 1 Jun 2017 15:25:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH 00/10] x86: undwarf unwinder

On Thu, Jun 01, 2017 at 07:47:05AM -0500, Josh Poimboeuf wrote:

> > It doesn't appear to be possible to get anywhere near a frame-pointer
> > unwinder due to having to do this log(n) lookup for every single
> > frame.
> 
> Hm, is there something faster, yet not substantially bigger?  Hash?
> Trie?

Not sure how to make a Hash work with nearest neighbour searches. And a
trie will only give you a constant speedup over the binary search but
not an improvement in complexity IIRC.