<s>
OpenACC	B-Operating_System
(	O
for	O
open	B-Operating_System
accelerators	I-Operating_System
)	O
is	O
a	O
programming	O
standard	O
for	O
parallel	B-Operating_System
computing	I-Operating_System
developed	O
by	O
Cray	O
,	O
CAPS	O
,	O
Nvidia	O
and	O
PGI	B-Application
.	O
</s>
<s>
The	O
standard	O
is	O
designed	O
to	O
simplify	O
parallel	B-Operating_System
programming	I-Operating_System
of	O
heterogeneous	O
CPU/GPU	O
systems	O
.	O
</s>
<s>
As	O
in	O
OpenMP	B-Application
,	O
the	O
programmer	O
can	O
annotate	O
C	B-Language
,	O
C++	B-Language
and	O
Fortran	B-Application
source	O
code	O
to	O
identify	O
the	O
areas	O
that	O
should	O
be	O
accelerated	O
using	O
compiler	O
directives	O
and	O
additional	O
functions	O
.	O
</s>
<s>
Like	O
OpenMP	B-Application
4.0	O
and	O
newer	O
,	O
OpenACC	B-Operating_System
can	O
target	O
both	O
the	O
CPU	B-General_Concept
and	O
GPU	B-Architecture
architectures	O
and	O
launch	O
computational	O
code	O
on	O
them	O
.	O
</s>
<s>
OpenACC	B-Operating_System
members	O
have	O
worked	O
as	O
members	O
of	O
the	O
OpenMP	B-Application
standard	O
group	O
to	O
merge	O
into	O
OpenMP	B-Application
specification	O
to	O
create	O
a	O
common	O
specification	O
which	O
extends	O
OpenMP	B-Application
to	O
support	O
accelerators	O
in	O
a	O
future	O
release	O
of	O
OpenMP	B-Application
.	O
</s>
<s>
These	O
efforts	O
resulted	O
in	O
a	O
technical	O
report	O
for	O
comment	O
and	O
discussion	O
timed	O
to	O
include	O
the	O
annual	O
Supercomputing	O
Conference	O
(	O
November	O
2012	O
,	O
Salt	O
Lake	O
City	O
)	O
and	O
to	O
address	O
non-Nvidia	O
accelerator	O
support	O
with	O
input	O
from	O
hardware	O
vendors	O
who	O
participate	O
in	O
OpenMP	B-Application
.	O
</s>
<s>
At	O
ISC’12	O
OpenACC	B-Operating_System
was	O
demonstrated	O
to	O
work	O
on	O
Nvidia	O
,	O
AMD	O
and	O
Intel	O
accelerators	O
,	O
without	O
performance	O
data	O
.	O
</s>
<s>
On	O
November	O
12	O
,	O
2012	O
,	O
at	O
the	O
SC12	O
conference	O
,	O
a	O
draft	O
of	O
the	O
OpenACC	B-Operating_System
version	O
2.0	O
specification	O
was	O
presented	O
.	O
</s>
<s>
New	O
suggested	O
capabilities	O
include	O
new	O
controls	O
over	O
data	O
movement	O
(	O
such	O
as	O
better	O
handling	O
of	O
unstructured	B-Application
data	I-Application
and	O
improvements	O
in	O
support	O
for	O
non-contiguous	O
memory	O
)	O
,	O
and	O
support	O
for	O
explicit	O
function	O
calls	O
and	O
separate	O
compilation	O
(	O
allowing	O
the	O
creation	O
and	O
reuse	O
of	O
libraries	O
of	O
accelerated	O
code	O
)	O
.	O
</s>
<s>
OpenACC	B-Operating_System
2.0	I-Operating_System
was	O
officially	O
released	O
in	O
June	O
2013	O
.	O
</s>
<s>
Support	O
of	O
OpenACC	B-Operating_System
is	O
available	O
in	O
commercial	O
compilers	O
from	O
PGI	B-Application
(	O
from	O
version	O
12.6	O
)	O
,	O
and	O
(	O
for	O
Cray	O
hardware	O
only	O
)	O
Cray	O
.	O
</s>
<s>
OpenUH	O
is	O
an	O
Open64	B-Application
based	O
open	O
source	O
OpenACC	B-Operating_System
compiler	O
supporting	O
C	B-Language
and	O
FORTRAN	B-Application
,	O
developed	O
by	O
HPCTools	O
group	O
from	O
University	O
of	O
Houston	O
.	O
</s>
<s>
OpenARC	O
is	O
an	O
open	O
source	O
C	B-Language
compiler	O
developed	O
at	O
Oak	O
Ridge	O
National	O
Laboratory	O
to	O
support	O
all	O
features	O
in	O
the	O
OpenACC	B-Operating_System
1.0	O
specification	O
.	O
</s>
<s>
An	O
experimental	O
open	O
source	O
compiler	O
,	O
accULL	O
,	O
is	O
developed	O
by	O
the	O
University	O
of	O
La	O
Laguna	O
(	O
C	B-Language
language	I-Language
only	O
)	O
.	O
</s>
<s>
of	O
University	O
of	O
Tsukuba	O
and	O
Programming	O
Environment	O
Research	O
Team	O
of	O
RIKEN	O
Center	O
for	O
Computational	O
Science	O
,	O
Japan	O
,	O
supported	O
OpenACC	B-Operating_System
,	O
and	O
combining	O
XcalableMP	O
and	O
OpenACC	B-Operating_System
.	O
</s>
<s>
IPMACC	O
is	O
an	O
open	O
source	O
C	B-Language
compiler	O
developed	O
by	O
University	O
of	O
Victoria	O
that	O
translates	O
OpenACC	B-Operating_System
to	O
CUDA	O
,	O
OpenCL	B-Application
,	O
and	O
ISPC	O
.	O
</s>
<s>
GCC	B-Application
support	O
for	O
OpenACC	B-Operating_System
was	O
slow	O
in	O
coming	O
.	O
</s>
<s>
A	O
GPU-targeting	O
implementation	O
from	O
Samsung	O
was	O
announced	O
in	O
September	O
2013	O
;	O
this	O
translated	O
OpenACC	B-Operating_System
1.1-annotated	O
code	O
to	O
OpenCL	B-Application
.	O
</s>
<s>
The	O
announcement	O
of	O
a	O
"	O
real	O
"	O
implementation	O
followed	O
two	O
months	O
later	O
,	O
this	O
time	O
from	O
NVIDIA	O
and	O
based	O
on	O
OpenACC	B-Operating_System
2.0	I-Operating_System
.	O
</s>
<s>
Experimental	O
support	O
for	O
OpenACC/PTX	O
did	O
end	O
up	O
in	O
GCC	B-Application
as	O
of	O
version	O
5.1	O
.	O
</s>
<s>
GCC6	O
and	O
GCC7	O
release	O
series	O
include	O
a	O
much	O
improved	O
implementation	O
of	O
the	O
OpenACC	B-Operating_System
2.0a	O
specification	O
.	O
</s>
<s>
GCC	B-Application
9.1	O
offers	O
nearly	O
complete	O
OpenACC	B-Operating_System
2.5	O
support	O
.	O
</s>
<s>
In	O
a	O
way	O
similar	O
to	O
OpenMP	B-Application
3.x	O
on	O
homogeneous	O
system	O
or	O
the	O
earlier	O
OpenHMPP	B-Application
,	O
the	O
primary	O
mode	O
of	O
programming	O
in	O
OpenACC	B-Operating_System
is	O
directives	O
.	O
</s>
<s>
The	O
specifications	O
also	O
include	O
a	O
runtime	B-Library
library	I-Library
defining	O
several	O
support	O
functions	O
.	O
</s>
<s>
To	O
exploit	O
them	O
,	O
user	O
should	O
include	O
"	O
openacc.h	O
"	O
in	O
C	B-Language
or	O
"	O
openacc_lib.h	O
"	O
in	O
Fortran	B-Application
;	O
and	O
then	O
call	O
acc_init( )	O
function	O
.	O
</s>
<s>
OpenACC	B-Operating_System
defines	O
an	O
extensive	O
list	O
of	O
pragmas	O
(	O
directives	O
)	O
,	O
for	O
example	O
:	O
</s>
<s>
Is	O
used	O
to	O
define	O
the	O
type	O
of	O
parallelism	B-Operating_System
in	O
a	O
parallel	O
or	O
kernels	O
region	O
.	O
</s>
<s>
There	O
are	O
some	O
runtime	O
API	B-Application
functions	I-Application
defined	O
too	O
:	O
acc_get_num_devices( )	O
,	O
acc_set_device_type( )	O
,	O
acc_get_device_type( )	O
,	O
acc_set_device_num( )	O
,	O
acc_get_device_num( )	O
,	O
</s>
<s>
OpenACC	B-Operating_System
generally	O
takes	O
care	O
of	O
work	O
organisation	O
for	O
the	O
target	O
device	O
however	O
this	O
can	O
be	O
overridden	O
through	O
the	O
use	O
of	O
gangs	O
and	O
workers	O
.	O
</s>
<s>
A	O
gang	O
consists	O
of	O
workers	O
and	O
operates	O
over	O
a	O
number	O
of	O
processing	O
elements	O
(	O
as	O
with	O
a	O
workgroup	O
in	O
OpenCL	B-Application
)	O
.	O
</s>
