linux-kernel - Re: [PATCH] modules: Take a shortcut for checking if an address is in a module

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Message-ID: <20080618095711.GC15255@elte.hu>
Date:	Wed, 18 Jun 2008 11:57:11 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Vegard Nossum <vegard.nossum@...il.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] modules: Take a shortcut for checking if an address is
	in a module


* Vegard Nossum <vegard.nossum@...il.com> wrote:

> >  > > Various pieces of the kernel (lockdep, latencytop, etc) tend to 
> >  > > store backtraces, sometimes at a relatively high frequency. In 
> >  > > itself this isn't a big performance deal (after all you're 
> >  > > using diagnostics features), but there have been some 
> >  > > complaints from people who have over 100 modules loaded that 
> >  > > this is a tad too slow.
> 
> Would it be overkill to simply drop the module addresses in an rbtree 
> and use that instead of a linear search over all the modules?
> 
> It would probably take a fair number of lines in C, and with a little 
> memory overhead, but the speed-up should be great. Should I give it a 
> try? (It would be arch-independent too.)

that's a tempting idea. rbtrees seem to be equally robust to plain lists 
in my experience, so i'd not find the extra complexity a showstopper, as 
long as the changes are well-tested. (radix trees on the other hand ... 
;-)

Rusty, Peter, Linus, any fundamental objections to Vegard's idea? Being 
able to take a transparent stack-trace signature for debugging or 
instrumentation purposes is important and performance does matter there 
IMO.

	Ingo
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