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SubjectRe: [PATCH] modules: Take a shortcut for checking if an address is in a module
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On Wed, 2008-06-18 at 11:57 +0200, Ingo Molnar wrote:
> * Vegard Nossum <vegard.nossum@gmail.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 ...
> ;-)

Radix trees are unsuited for this application, esp in their current
implementation.

> 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.

A tree makes sense, although if more archs can do the same Arjan did for
x86 that'd be even better.



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