On Do, 2008-07-10 at 19:08 +0400, Vladimir Prus wrote:
SD wrote:
# Create libtest.so g++ -shared -fPIC test.cpp -o libtest.so # link boost_regex before libtest.so g++ main.cpp -lboost_regex${BOOST_EXT} -ltest -L${PWD} -o main_fast # link boost_regex after libtest.so g++ main.cpp -ltest -lboost_regex${BOOST_EXT} -L${PWD} -o main_slow
time env LD_LIBRARY_PATH=${PWD} ./main_slow # real 0m0.753s, user 0m0.746s, sys 0m0.004s time env LD_LIBRARY_PATH=${PWD} ./main_fast # real 0m0.104s, user 0m0.103s, sys 0m0.002s
As the results show the order which libs are being linked to the program has significant performance impacts on execution time: main_fast is about 7 times faster than main_slow. .... I would appreciate if someone could explain these surprising results.
Before we go on guessing what could cause this -- do you get the same timings on successive runs of any given executable?
Yes, the runtimes vary only minimally.
Does running ldd on both binaries report that the same boost_regexp binary is being linked to? I don't see why different ones would be linked to, but still.
If this theory is wrong, can you create a self-contained archive with all the necessary files, and send it, so that I (and others) can try to reproduce. This sounds truly bizarre.
- Volodya
$ LD_LIBRARY_PATH=./ ldd ./main_slow linux-vdso.so.1 => (0x00007fff1bbff000) libtest.so => ./libtest.so (0x00007ffc136fd000) libboost_regex.so => /usr/lib/libboost_regex.so (0x00007ffc1346b000) libstdc++.so.6 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.1/libstdc++.so.6 (0x00007ffc13168000) libm.so.6 => /lib/libm.so.6 (0x00007ffc12ee8000) libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00007ffc12cd2000) libc.so.6 => /lib/libc.so.6 (0x00007ffc12992000) /lib64/ld-linux-x86-64.so.2 (0x00007ffc13914000) $ LD_LIBRARY_PATH=./ ldd ./main_fast linux-vdso.so.1 => (0x00007ffffe9fe000) libboost_regex.so => /usr/lib/libboost_regex.so (0x00007f88f636f000) libtest.so => ./libtest.so (0x00007f88f6158000) libstdc++.so.6 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.1/libstdc++.so.6 (0x00007f88f5e55000) libm.so.6 => /lib/libm.so.6 (0x00007f88f5bd5000) libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00007f88f59bf000) libc.so.6 => /lib/libc.so.6 (0x00007f88f567f000) /lib64/ld-linux-x86-64.so.2 (0x00007f88f6601000) As you can see, the only difference seems to be the position of libtest.so and libboost_regex.so, whereas in the fast version libboost_regex is linked in first. I've attached 4 files. You can run ./runtest.sh in the directory to run the tests. Regards Stefan