mattst88's blog - The Case for Open Sourcing Alpha-Optimized Libraries

The Case for Open Sourcing Alpha-Optimized Libraries

As long as I've been interested in Alpha hardware, I've been intrigued by Compaq's Alpha-optimized compilers and libraries. In some cases, the compilers produce code multiple times faster than by gcc. The math library, libcpml, contains functions that execute in half the time of their glibc equivalents. Since the abandonment of the Alpha platform, this code has languished. In some cases, the performance gap between Compaq's tools and their open source counterparts has shrunk. In others, the benefits of hand-tuned assembly still shine. This prompted me to contact HP and request the release of the code. They unfortunately concluded that an old MIPS license prevented them from releasing the compilers. I've recently contacted HP once again to persuade them to release libcpml and libots as free software, as libraries containing nothing but hand-tuned Alpha assembly could not be encumbered by this license. I also attached the following benchmarks as evidence of why this code is still valuable so many years after it was written.

Using a test suite I wrote, I benchmarked the implementation of math functions found in glibc with those in libcpml.

Function	Library	Run 1	Run 2	Run 3	Run 4	Run 5	Run 6	Run 7	Run 8	Run 9	Run 10	Average	Speed Up (cpml over glibc)
sin	glibc	311	292	312	310	297	304	307	300	312	312	305.11
sin	cpml	156	155	148	150	152	154	152	151	151	163	152.89	99.56%
cos	glibc	251	246	245	243	392	251	240	240	252	240	261
cos	cpml	156	151	153	160	159	160	146	149	151	157	154	69.48%
tan	glibc	9384	9345	9351	9252	9195	9273	9237	9272	9213	9239	9264.11
tan	cpml	172	169	168	166	168	173	170	176	183	175	172	5286.11%
sinh	glibc	305	296	296	302	291	295	437	295	294	298	311.56
sinh	cpml	141	136	140	139	135	139	137	140	136	139	137.89	125.95%
cosh	glibc	352	327	316	363	351	338	352	358	329	362	344
cosh	cpml	138	139	137	141	140	142	138	138	144	138	139.67	146.29%
tanh	glibc	260	258	270	260	266	260	263	257	265	256	261.67
tanh	cpml	212	203	199	203	203	198	210	195	212	198	202.33	29.33%
asin	glibc	1434	1197	1227	1300	1346	1323	1390	1227	1274	1244	1280.89
asin	cpml	627	611	581	641	612	596	660	586	620	692	622.11	105.89%
acos	glibc	1034	1207	1054	1015	1015	1031	1068	994	1051	964	1044.33
acos	cpml	621	625	657	635	610	638	587	623	617	614	622.89	67.66%
atan	glibc	932	860	904	904	866	902	948	879	908	880	894.56
atan	cpml	566	536	538	519	538	513	521	533	526	497	524.56	70.54%
asinh	glibc	784	743	749	741	742	773	751	726	784	743	750.22
asinh	cpml	519	513	506	494	527	494	494	529	495	510	506.89	48.00%
acosh	glibc	912	866	855	785	990	823	865	820	845	836	853.89
acosh	cpml	954	912	898	946	905	904	898	920	928	885	910.67	-6.23%
atanh	glibc	1125	1939	1071	1053	1079	1085	1068	996	1062	1143	1166.22
atanh	cpml	875	898	851	828	912	864	843	871	1355	851	919.22	26.87%
floor	glibc	88	82	82	79	76	91	87	84	84	86	83.44
floor	cpml	121	123	128	120	121	119	117	120	126	112	120.67	-30.85%
ceil	glibc	89	90	85	85	86	79	81	80	81	80	83
ceil	cpml	123	117	115	114	131	114	119	114	122	118	118.22	-29.79%
round	glibc	102	77	78	90	85	87	77	83	85	84	82.89
round	cpml	366	111	115	102	118	112	108	107	109	111	110.33	-24.87%
trunc	glibc	84	83	87	89	77	84	82	85	85	84	84
trunc	cpml	118	120	118	117	116	119	112	109	114	110	115	-26.96%
log	glibc	790	764	767	763	768	768	732	739	744	747	754.67
log	cpml	502	456	476	476	465	460	922	484	481	456	519.56	45.25%
log10	glibc	840	803	808	802	784	856	785	782	774	826	802.22
log10	cpml	527	534	549	551	536	578	535	530	540	537	543.33	47.65%
log2	glibc	493	499	522	504	478	504	519	495	499	539	506.56
log2	cpml	520	493	514	509	481	520	493	493	493	728	524.89	-3.49%
log1p	glibc	233	240	235	224	234	230	227	228	229	233	231.11
log1p	cpml	304	279	276	297	269	299	291	291	305	286	288.11	-19.78%
exp	glibc	401	357	357	403	344	407	413	475	372	401	392.11
exp	cpml	130	138	132	128	133	139	124	130	137	126	131.89	197.30%
expm1	glibc	225	205	218	208	214	213	216	211	221	208	212.67
expm1	cpml	160	165	169	157	166	162	157	164	165	157	162.44	30.92%
exp2	glibc	1339	1314	1327	1305	1339	1310	1284	1284	1334	1309	1311.78
exp2	cpml	151	149	136	140	148	137	139	149	138	138	141.56	826.66%

As can be seen, many math (especially trigonometric) functions are 50-200% faster in libcpml. In other cases, such as the rounding functions, glibc is faster.

A few notes:

Testing was done on my UP1500 with an 800 MHz EV68AL, 8MB L2 cache, and 4 GB RAM
It may not be fair to benchmark ceil/floor as their implementations in glibc are not correct
I don't entirely trust the glibc tan results, as they appear to be 50x slower than libcpml

As more evidence of libcpml's superiority, by simply linking nbench with -lcpml instead of -lm, the fourier benchmark gets a speed up of 2.5x to 3.0x.

If you'd like to run this test yourself, here's how. (I assume you run Gentoo on your Alpha.)

Download libcpml for your processor, EV5, EV6 or later

Add the libcpml ebuild to your portage overlay

svn co svn://mattst88.com/svn/compaq-c-overlay/

Install libcpml (and its libots dependency) and make sure to set the ev6 USE flag if your Alpha is an EV6

Checkout the test suite with

svn co svn://mattst88.com/svn/cpml-benchmarks

Edit the CFLAGS variable in Makefile for your processor
Run
```
make test
```
from the cpml-benchmarks folder
A results.csv file is generated in the cpml-benchmarks folder. Analyze results using a Spreadsheet program

If you like, email the results to me. I'd like to see what these benchmarks look like on an EV5 machine.

11 January 2009 – Tags: alpha linux