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| author | Alexander van Heukelum <heukelum@mailshack.com> | 2008-03-09 21:01:04 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-04-26 19:21:16 +0200 |
| commit | 6fd92b63d0626a8fe7eb8e2e50d19ecaa18cb412 (patch) | |
| tree | 840f6cf998c251cdfcae37a03f34b34ac5bea3a5 /lib | |
| parent | 18e413f7193ed2f6991d959863f46330813aa242 (diff) | |
| download | lwn-6fd92b63d0626a8fe7eb8e2e50d19ecaa18cb412.tar.gz lwn-6fd92b63d0626a8fe7eb8e2e50d19ecaa18cb412.zip | |
x86: change x86 to use generic find_next_bit
The versions with inline assembly are in fact slower on the machines I
tested them on (in userspace) (Athlon XP 2800+, p4-like Xeon 2.8GHz, AMD
Opteron 270). The i386-version needed a fix similar to 06024f21 to avoid
crashing the benchmark.
Benchmark using: gcc -fomit-frame-pointer -Os. For each bitmap size
1...512, for each possible bitmap with one bit set, for each possible
offset: find the position of the first bit starting at offset. If you
follow ;). Times include setup of the bitmap and checking of the
results.
Athlon Xeon Opteron 32/64bit
x86-specific: 0m3.692s 0m2.820s 0m3.196s / 0m2.480s
generic: 0m2.622s 0m1.662s 0m2.100s / 0m1.572s
If the bitmap size is not a multiple of BITS_PER_LONG, and no set
(cleared) bit is found, find_next_bit (find_next_zero_bit) returns a
value outside of the range [0, size]. The generic version always returns
exactly size. The generic version also uses unsigned long everywhere,
while the x86 versions use a mishmash of int, unsigned (int), long and
unsigned long.
Using the generic version does give a slightly bigger kernel, though.
defconfig: text data bss dec hex filename
x86-specific: 4738555 481232 626688 5846475 5935cb vmlinux (32 bit)
generic: 4738621 481232 626688 5846541 59360d vmlinux (32 bit)
x86-specific: 5392395 846568 724424 6963387 6a40bb vmlinux (64 bit)
generic: 5392458 846568 724424 6963450 6a40fa vmlinux (64 bit)
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/find_next_bit.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/lib/find_next_bit.c b/lib/find_next_bit.c index 78ccd73a8841..5820e072b890 100644 --- a/lib/find_next_bit.c +++ b/lib/find_next_bit.c @@ -15,6 +15,8 @@ #include <asm/byteorder.h> #define BITOP_WORD(nr) ((nr) / BITS_PER_LONG) +#undef find_next_bit +#undef find_next_zero_bit /** * find_next_bit - find the next set bit in a memory region |