Slowdown with randomize_va_space in 2.6.12.2

[Paulo Marques <pmarques@grupopie.com>]

Hi, all

I have a bash script that calls a small application several times 
(around 50 calls) that just send and receives data through an already 
open tcp socket to a local server through the loopback device. It also 
launches another small app several times that just reads a small file 
from disk and does some processing on it in memory.

We noticed a severe performance regression on this application under 
kernel 2.6.12.2 that we tracked down to the address space randomization 
patches:

# echo 0 > randomize_va_space
# time ./script
real    0m0.671s
user    0m0.293s
sys     0m0.325s

# echo 1 > randomize_va_space
# time ./script
real    0m3.310s
user    0m2.712s
sys     0m0.401s

Notice that the real time is 5x slower with "randomize_va_space" turned 
on. This is on a Transmeta Crusoe TM5600 at 533MHz.

What is weird is that most of the extra time is being accounted as 
user-space time, but the user-space application is exactly the same in 
both runs, only the "randomize_va_space" parameter changed.

I browsed the randomization patch code and I don't think the random 
calculations themselves could account for all that time.

Does anybody have a clue as to why this is happening or what I should do 
to debug this further?

-- 
Paulo Marques - www.grupopie.com

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