strlen

Variants

Name	Description
stock	MD amd64 version {{rep stosq}}
SSE2	movdqu for block-store
SSE2 aligned	movaps for aligned block-store and movdqu for unaligned
AVX 128	128-bit vmovdqu for block-store
AVX 256	256-bit vmovdqu for block-store
ERMS	repne stosb for machines with ERMS

Machines Tested

CPU	Speed (GHz)	Notes
AMD FX-8120	3.11	1 x 8 zoo.freebsd.org
AMD Opteron 6328	3.20	2 x 8 Supermicro H8DG6/H8DGi
Intel Xeon X5365	3.00	2 x 4 Supermicro X7DBU
Intel Xeon X5482	3.20	2 x 4 Supermicro X7DWN+
Intel Xeon X5675	3.07	Westmere 2 x 6 Supermicro X8DTU
Intel Core i5-2520M	2.50	Sandy Bridge 1 x 4 Thinkpad X220 (4286)
Intel Core i5-2500K	3.30	Sandy Bridge 1 x 4 MSI Z77A-G45 (MS-7752)
Intel Xeon E5-2680	2.70	Romley 2 x 8 Supermicro X9DRW
Intel Xeon E5-2667 v2	3.30	Romley V2 2 x 8 Supermicro X9DRW (supports ERMS)

Test Cases

Name	Description
page	set page to 0xa5
short	set aligned 15 bytes to 0xa5
short2	set aligned 32 bytes to 0xa5
short3	set aligned 48 bytes to 0xa5
offset	set misaligned ( + 4) 128 bytes to 0
offset2	set misaligned ( + 7) 97 bytes to 0

Results

The numbers are the min value in the distribution where the values are a TSC delta across a single invocation of the test.

Bold indicates the lowest time among the given variations in a Test and CPU combination. Green text is used for times faster than the stock implementation, and red text is used for times slower than the stock implementation.

CPU	Test / Variant
	page						short						short2						short3						offset						offset2
	stock	SSE2	SSSE2 aligned	AVX 128	AVX 256	ERMS	stock	SSE2	SSSE2 aligned	AVX 128	AVX 256	ERMS	stock	SSE2	SSSE2 aligned	AVX 128	AVX 256	ERMS	stock	SSE2	SSSE2 aligned	AVX 128	AVX 256	ERMS	stock	SSE2	SSSE2 aligned	AVX 128	AVX 256	ERMS	stock	SSE2	SSSE2 aligned	AVX 128	AVX 256	ERMS
AMD FX-8120
AMD Opteron 6328
Intel Xeon X5365
Intel Xeon X5482
Intel Xeon X5675
Intel Core i5-2520M
Intel Core i5-2500K
Intel Xeon E5-2680
Intel Xeon E5-2667 v2

Conclusions