Please not that using svn_log without giving revisions is much, much slower then with revisions. Examples:
$ time php -r "svn_log('http://localhost/svn/shopadsl');"
real 0m2.140s
user 0m0.140s
sys 0m0.000s
VS
$ time php -r "svn_log('http://localhost/svn/shopadsl', 0, 45);"
real 0m0.063s
user 0m0.024s
sys 0m0.016s