linux-kernel - Re: module: Speed up symbol resolution during module loading

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Message-Id: <200909240938.54063.rusty@rustcorp.com.au>
Date:	Thu, 24 Sep 2009 09:38:53 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
Cc:	"linux-kernel" <linux-kernel@...r.kernel.org>,
	linux-kbuild@...r.kernel.org, linux-modules@...r.org,
	Sam Ravnborg <sam@...nborg.org>
Subject: Re: module: Speed up symbol resolution during module loading

On Thu, 24 Sep 2009 02:22:15 am Alan Jenkins wrote:
> [CC to lkml fixed :-/]
> 
> Rusty Russell wrote:
> > On Tue, 22 Sep 2009 10:58:28 pm Alan Jenkins wrote:
> >   
> >> The following series applies against v2.6.31. It sorts the tables of builtin
> >> symbols, so the module loader can resolve them using a binary search.
> >>
> >> The kbuild changes to achieve this are less scary than I expected.  I'm
> >> optimistic that they can be accepted without radical alteration :-).
> >>
> >> Quoting from the last patch in this series:
> >>
> >> "On my EeePC 701, coldplug is mainly cpu bound and takes 1.5 seconds
> >> during boot. perf showed this change eliminated 20% of cpu cycles during
> >> coldplug, saving 0.3 seconds of real time.
> >>     
> >
> > Hi Alan,
> >
> >    This seems useful, but wouldn't it be simpler to just sort at boot time?
> > The same could be done for modules, possibly reducing code.
> >
> > Alternately, there's a standard way of hashing ELF symbols, but I'm not sure
> > we can convince the linker to generate it for vmlinux (I haven't looked
> > though).
> >
> > Thanks!
> > Rusty.
> >   
> 
> I'm concerned that people would object to the extra overhead at boot
> time.  I've hacked up a prototype to sort at boot time and it takes 7ms
> on the same hardware.

OK, that seems a lot to me.  Fair enough; if Sam acks the build parts, I'll
put it in my tree.  A bit late for this merge window though.

Thanks!
Rusty.
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