prelink: is it worth it?

[yersinia]

On Thu, Jul 9, 2009 at 4:55 PM, Ulrich Drepper <drepper at redhat.com> wrote:

> Adam Miller wrote:
> > I am curious as to this answer as well because prelink has been
> > something that actually hurt my netbook in performance so I nuked it.
>
> Performance only ever can be hurt because prelink runs periodically to
> prelink newly installed code or re-randomize to increase security.
>
> prelink has two benefits:
>
> - almost all relocations a program has to perform are avoided.  These
>  can be very expensive when many dependencies and/or large symbol
>  tables are involved.  The latter is somewhat mitigated by the new
>  symbol table hashing we implemented some time back but still.
>
> - as a side effect of the first point some pages in the loaded binary
>  are not copied-on-write.  This can obviously have good effects on
>  systems with little memory (netbooks).
>
>
> Just run your own tests on apps with many relocations and dependencies.
>  FF, OO.org, most GUI apps come into mind.  Use
>
>  LD_DEBUG=statistics some/program
>
> to compare numbers.  Run it with and without prelink (but always with
> hot disk cache to be fair).  The number of cycles for total startup is
> representative of the win.
>
> Note, also small but frequently used apps benefit.  I run gcc etc a lot
> and like every single saved cycle.
>

But something one have to pay a security prize on not disabling it :  it
render impossible to have a
centralizzated security integrity management (e.g. rfc.sf.net for example)
or one have to skip from check the prelink binary. Very bad i think.

>
> --
> ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
>
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