If you have the default Apache page installed on your web server, then mod_negotiate is going to be helpful and try to serve the content in the flavor and language your browser prefers. This of course comes at a hefty cost:
$ dtrace -ppgrep httpd -s shibby.d
dtrace: script 'shibby.d' matched 4 probes
^C
memcpy 2824
apr_file_read 2496
$ cat shibby.d
pid$target::memcpy:entry
{
@memcpy[probefunc] = count();
}
pid$target::apr_file_read:entry
{
@apr_file_read[probefunc] = count();
}
I came across this while looking for the busiest functions in Apache (this of course is not the case with normal pages).