# OpenCL

OpenCL is a cross-platform interface to compute devices.

# 1 Implementations

# 1.1 PoCL

PoCL is an implementation of OpenCL for CPU devices based on LLVM.

# 1.2 Clover

Clover is Mesa’s original OpenCL implementation based on LLVM.

# 1.3 rusticl

Mesa rusticl is an implementation of OpenCL for GPU devices based on LLVM.

AND RX 580 needs environment variable RUSTICL_ENABLE=radeonsi.

Support for double precision is “experimental”, enable it by setting the environment variable RUSTICL_FEATURES=fp64.

# 1.4 PoCL vs Clover vs rusticl

Unfortunately (at least on Debian Trixie), using both PoCL and Clover or rusticl at the same time causes crashes, possibly because both are based on LLVM and LLVM’s internal state gets confused. Might be exacerbated if different LLVM versions are used.

Make sure only one of pocl.icd and rusticl.icd is present in /etc/OpenCL/vendors (you can rename pocl.icd to pocl.icd.disabled, for example).

# 2 Benchmarks

# 2.1 Fraktaler-3

Using fraktaler-3 wisdom benchmark:

machine	backend	float	double	floatexp	doubleexp	softfloat	long double	float128	notes
eiskaffee	CPU	18.99	18.90	13.05	12.80	12.91	16.57	12.78	long double is x87
“	Clover	22.37	21.19	17.90	16.83	17.48	-	-
“	rusticl	20.30	19.84	18.37	15.21	15.53	-	-
decaf	CPU	19.58	19.83	12.99	13.06	13.32	16.69	14.15	long double is x87
“	PoCL	19.25	19.62	14.84	14.63	15.06	-	-
“	rusticl	20.66	19.56	18.75	17.05	-	-	-
tallat	CPU	11.51	11.46	5.52	5.33	5.88	9.51	5.71	long double is x87
“	PoCL	10.60	10.90	7.48	7.47	7.22	-	-
phone cat	CPU	16.40	16.22	10.72	10.75	11.41	10.15	-	long double is float128
phone uk	CPU	10.76	10.73	7.45	7.27	7.87	10.84	-	long double is double

Higher is better, increase of 1 unit means 2 times faster.