Strange slowdown of zlib.

[Ian Lepore]

On Thu, 2014-06-19 at 17:44 +0200, Magnus Nilsson wrote:
> I have the strangest behaviour of zlib on FreeBSD 8.2 (ARM, but I don't
> think it's necessarily an ARM specific issue).
> Doing
> # md5 /lib/libz.so.5
> or
> # cp /lib/libz.so.5 /tmp/
> # export LD_LIBRARY_PATH=/tmp/
> slows down applications (I've tested bsdtar and gzip) using zlib to a crawl
> on my system.
> 
> In the later case, doing
> # unset LD_LIBRARY_PATH
> reverts the issue.
> However, I haven't found any way to recover from the first case, apart from
> rebooting - then the execution time is back to normal.
> 
> Here is a log of what I describe above (first moving zlib, then doing the
> md5):
> # cp some2MBfile /tmp/
> # time gzip /tmp/some2MBfile
> real    0m0.325s
> user    0m0.284s
> sys     0m0.037s
> # rm /tmp/some2MBfile.gz
> # cp /lib/libz.so.5 /tmp/
> # export LD_LIBRARY_PATH=/tmp/
> # cp some2MBfile /tmp/
> # time gzip /tmp/some2MBfile
> real    0m11.949s
> user    0m11.635s
> sys     0m0.035s
> # rm /tmp/some2MBfile.gz
> # unset LD_LIBRARY_PATH
> # cp some2MBfile /tmp/
> # time gzip /tmp/some2MBfile
> real    0m0.325s
> user    0m0.288s
> sys     0m0.035s
> # rm /tmp/some2MBfile.gz
> # md5 /lib/libz.so.5
> # cp some2MBfile /tmp/
> # time gzip /tmp/some2MBfile
> real    0m11.919s
> user    0m11.608s
> sys     0m0.031s
> # rm /tmp/some2MBfile.gz
> 
> Do you have any idea what could be going on?
> Any clues are welcome.
> 
> Kind regards/Magnus

This is a known problem on armv4/v5 in freebsd 8.  Here is some archived
info on it including patches that work around the problem (rather
crudely, but good enough for our needs at $work).

http://lists.freebsd.org/pipermail/freebsd-arm/2012-January/003288.html

-- Ian