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

Note: clang was too smart and inlined all the short memset calls, so I had to create a copy of the amd64 version called memset_stock() to fool it.

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	1078	987	972	974	3095	1009	157	161	157	157	157	157	188	99	90	97	91	248	203	89	119	95	119	290	265	89	96	97	148	469	221	122	122	120	144	469
AMD Opteron 6328	482	443	424	461	2454	449	69	106	106	106	106	106	68	87	88	86	87	128	66	90	92	90	89	151	102	89	95	95	99	230	104	92	93	93	98	226
Intel Xeon X5365	657	1206	378	--	--	720	144	144	144	--	--	144	126	90	90	--	--	162	126	99	90	--	--	171	243	135	135	--	--	252	126	108	108	--	--	225
Intel Xeon X5482	624	1144	312	--	--	696	32	112	112	--	--	112	32	64	64	--	--	128	32	72	64	--	--	144	56	120	120	--	--	224	56	96	104	--	--	200
Intel Xeon X5675	352	296	300	--	--	428	24	100	100	--	--	96	46	83	92	--	--	120	24	83	48	--	--	136	99	56	106	--	--	192	48	99	106	--	--	160
Intel Core i5-2520M	1812	962	962	950	1400	13100	87	350	350	350	350	337	87	162	162	150	600	400	87	162	162	150	562	450	87	187	187	187	625	700	87	187	187	187	637	612
Intel Core i5-2500K	734	635	635	627	924	907	222	231	231	231	231	222	156	107	107	99	396	264	156	107	107	99	404	297	453	123	123	123	412	420	156	123	123	123	420	354
Intel Xeon E5-2680	356	308	308	304	452	440	28	112	112	112	112	112	28	52	52	48	196	132	28	52	52	48	196	148	56	60	60	60	200	204	52	60	60	60	204	176
Intel Xeon E5-2667 v2	428	344	344	340	494	292	24	60	60	60	60	60	24	84	84	84	228	60	24	84	88	84	228	56	52	96	96	92	232	60	48	64	64	64	208	60

Conclusions