Date: Tue, 15 Aug 2006 16:04:00 +0800 From: "Intron" <mag@intron.ac> To: Brooks Davis <brooks@one-eyed-alien.net> Cc: freebsd-hackers@freebsd.org Subject: Re: The optimization of malloc(3): FreeBSD vs GNU libc Message-ID: <courier.44E17FF0.00006B85@intron.ac> In-Reply-To: <20060814231504.GB69362@lor.one-eyed-alien.net> References: <courier.44E102F7.00004C34@intron.ac> <20060814231504.GB69362@lor.one-eyed-alien.net>
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Brooks Davis wrote: > On Tue, Aug 15, 2006 at 07:10:47AM +0800, Intron wrote: >> One day, a friend told me that his program was 3 times slower under >> FreeBSD 6.1 than under GNU/Linux (from Redhat 7.2 to Fedora Core 5). >> I was astonished by the real repeatable performance difference on >> AMD Athlon XP 2500+ (1.8GHz, 512KB L2 Cache). >> >> After hacking, I found that the problem is nested in malloc(3) of >> FreeBSD libc. >> >> Download the testing program: http://ftp.intron.ac/tmp/fdtd.tar.bz2 >> >> You may try to compile the program WITHOUT the macro "MY_MALLOC" >> defined (in Makefile) to use malloc(3) provided by FreeBSD 6.1. >> Then, time the running of the binary (on Athlon XP 2500+): >> >> #/usr/bin/time ./fdtd.FreeBSD 500 500 1000 >> ... >> 165.24 real 164.19 user 0.02 sys >> >> Please try to recompile the program (Remember to "make clean") >> WITH the macro "MY_MALLOC" defined (in Makefile) to use my own >> simple implementation of malloc(3) (i.e. my_malloc() in cal.c). >> And time the running again: >> >> #/usr/bin/time ./fdtd.FreeBSD 500 500 1000 >> ... >> 50.41 real 49.95 user 0.04 sys >> >> You may repeat this testing again and again. >> >> I guess this kind of performance difference comes from: >> >> 1. His program uses malloc(3) to obtain so many small memory blocks. >> >> 2. In this case, FreeBSD malloc(3) obtains small memory blocks from >> kernel and pass them to application. >> >> But malloc(3) of GNU libc obtains large memory blocks from kernel >> and splits & reallocates them in small blocks to application. >> >> You may verify my judgement with truss(1). >> >> 3. The way of FreeBSD malloc(3) makes VM page mapping too chaotic, which >> reduces the efficiency of CPU L2 Cache. In contrast, my my_malloc() >> simulates the behavior of GNU libc malloc(3) partially and avoids >> the over-chaos. >> >> Callgrind is broken under FreeBSD, or I will verify my guess with it. >> >> I have also verified the program on Intel Pentium 4 511 (2.8GHz, 1MB >> L2 cache, running FreeBSD 6.1 i386 though this CPU supports EM64T) >> >> >/usr/bin/time ./fdtd.FreeBSD 500 500 1000 >> ... >> 185.30 real 184.28 user 0.02 sys >> >> >/usr/bin/time ./fdtd.FreeBSD 500 500 1000 >> ... >> 36.31 real 35.94 user 0.03 sys >> >> NOTE: you probably cannot see the performance difference on CPU with >> small L2 cache such as Intel Celeron 1.7GHz with 128 KB L2 Cache. > > In CURRENT we've replaced phkmalloc with jemalloc. It would be useful > to see how this benchmark performs with that. I believe it does similar > things. > > -- Brooke You're right. Now with truss(1) I can see that malloc(3) on 7.0-CURRENT (4 days ago) calls brk(2) to obtain 2MB each time. I will continue my testing. ------------------------------------------------------------------------ From Beijing, China
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