BMC/Intel-BMC/linux.git - Intel OpenBMC Linux kernel source tree (mirror)

Age	Commit message (Collapse)	Author	Files	Lines
2010-05-18	x86, hweight: Use a 32-bit popcnt for __arch_hweight32()	H. Peter Anvin	1	-4/+6
	Use a 32-bit popcnt instruction for __arch_hweight32(), even on x86-64. Even though the input register will usually be zero-extended due to the standard operation of the hardware, it isn't necessarily so if the input value was the result of truncating a 64-bit operation. Note: the POPCNT32 variant used on x86-64 has a technically unnecessary REX prefix to make it five bytes long, the same as a CALL instruction, therefore avoiding an unnecessary NOP. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> Cc: Borislav Petkov <borislav.petkov@amd.com> LKML-Reference: <alpine.LFD.2.00.1005171443060.4195@i5.linux-foundation.org>
2010-04-07	x86: Add optimized popcnt variants	Borislav Petkov	1	-0/+59
	Add support for the hardware version of the Hamming weight function, popcnt, present in CPUs which advertize it under CPUID, Function 0x0000_0001_ECX[23]. On CPUs which don't support it, we fallback to the default lib/hweight.c sw versions. A synthetic benchmark comparing popcnt with __sw_hweight64 showed almost a 3x speedup on a F10h machine. Signed-off-by: Borislav Petkov <borislav.petkov@amd.com> LKML-Reference: <20100318112015.GC11152@aftab> Signed-off-by: H. Peter Anvin <hpa@zytor.com>