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alpha: simplify and optimize sched_find_first_bit 

Search only the first 100 bits instead of 140, saving a couple
instructions. The resulting code is about 1/3 faster (40K ticks/1000
iterations down to 30K ticks/1000 iterations).

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: linux-alpha@vger.kernel.org
Acked-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Matt Turner 2010-04-28 22:49:36 -04:00 committed by Matt Turner
parent 1cb3d8e2c8
commit a75f5f0f0a
1 changed files with 9 additions and 11 deletions
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20
arch/alpha/include/asm/bitops.h
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@ -438,22 +438,20 @@ static inline unsigned int __arch_hweight8(unsigned int w)
/* /*
* Every architecture must define this function. It's the fastest * Every architecture must define this function. It's the fastest
* way of searching a 140-bit bitmap where the first 100 bits are * way of searching a 100-bit bitmap. It's guaranteed that at least
* unlikely to be set. It's guaranteed that at least one of the 140 * one of the 100 bits is cleared.
* bits is set.
*/ */
static inline unsigned long static inline unsigned long
sched_find_first_bit(unsigned long b[3]) sched_find_first_bit(const unsigned long b[2])
{ {
unsigned long b0 = b[0], b1 = b[1], b2 = b[2]; unsigned long b0, b1, ofs, tmp;
unsigned long ofs;
ofs = (b1 ? 64 : 128); b0 = b[0];
b1 = (b1 ? b1 : b2); b1 = b[1];
ofs = (b0 ? 0 : ofs); ofs = (b0 ? 0 : 64);
b0 = (b0 ? b0 : b1); tmp = (b0 ? b0 : b1);
return __ffs(b0) + ofs; return __ffs(tmp) + ofs;
} }
#include <asm-generic/bitops/ext2-non-atomic.h> #include <asm-generic/bitops/ext2-non-atomic.h>