linux performance puzzle

Hi all,

I have a program that reads 100000 lines from stdin, performs
processing in two worker threads (there are two processors on my
system), and outputs the result into a file. To make the test
cleaner, I excluded all file operations by reading from a pipe
(created by another small program I wrote), and redirecting the output
into /dev/null.

Now the puzzle: while it generally takes about 11.5 sec to execute my
test, the first run after rebuild takes _significantly_ more,
sometimes 19 sec, sometimes 15, etc. All the subsequent runs
consistently take around 11.5 sec.

I noted that I actually need to rebuild -- just touching the
executable does not have the same effect.

I am not using any shared objects that need to be downloaded over the
network.

My system is:
Red Hat Enterprise Linux WS release 4 (Nahant Update 2)

Can anybody suggest any explanation of this?

Thanks in advance,
Arkadiy
.

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