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Commit a75f5f0f authored by Matt Turner's avatar Matt Turner Committed by Matt Turner
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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: default avatarRichard Henderson <rth@twiddle.net>
Signed-off-by: default avatarMatt Turner <mattst88@gmail.com>
parent 1cb3d8e2

arch/alpha/include/asm/bitops.h

+9 −11
Original line number Diff line number Diff line
@@ -438,22 +438,20 @@ static inline unsigned int __arch_hweight8(unsigned int w) 


/*

 * Every architecture must define this function. It's the fastest

 * way of searching a 140-bit bitmap where the first 100 bits are

 * unlikely to be set. It's guaranteed that at least one of the 140

 * bits is set.

 * way of searching a 100-bit bitmap.  It's guaranteed that at least

 * one of the 100 bits is cleared.

 */

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 ofs;

	unsigned long b0, b1, ofs, tmp;



	ofs = (b1 ? 64 : 128);

	b1 = (b1 ? b1 : b2);

	ofs = (b0 ? 0 : ofs);

	b0 = (b0 ? b0 : b1);

	b0 = b[0];

	b1 = b[1];

	ofs = (b0 ? 0 : 64);

	tmp = (b0 ? b0 : b1);



	return __ffs(b0) + ofs;

	return __ffs(tmp) + ofs;

}



#include <asm-generic/bitops/ext2-non-atomic.h>