<s>
DOACROSS	B-General_Concept
parallelism	I-General_Concept
is	O
a	O
parallelization	B-Operating_System
technique	O
used	O
to	O
perform	O
Loop-level	B-Operating_System
parallelism	I-Operating_System
by	O
utilizing	O
synchronisation	O
primitives	O
between	O
statements	O
in	O
a	O
loop	O
.	O
</s>
<s>
This	O
technique	O
is	O
used	O
when	O
a	O
loop	O
cannot	O
be	O
fully	O
parallelized	B-Operating_System
by	O
DOALL	O
parallelism	B-Operating_System
due	O
to	O
data	O
dependencies	O
between	O
loop	O
iterations	O
,	O
typically	O
loop-carried	O
dependencies	O
.	O
</s>
<s>
Therefore	O
,	O
DOACROSS	B-General_Concept
parallelism	I-General_Concept
can	O
be	O
used	O
to	O
complement	O
DOALL	O
parallelism	B-Operating_System
to	O
reduce	O
loop	O
execution	O
times	O
.	O
</s>
<s>
DOACROSS	B-General_Concept
parallelism	I-General_Concept
is	O
particularly	O
useful	O
when	O
one	O
statement	O
depends	O
on	O
the	O
values	O
generated	O
by	O
another	O
statement	O
.	O
</s>
<s>
In	O
such	O
a	O
loop	O
,	O
DOALL	O
parallelism	B-Operating_System
can	O
not	O
be	O
implemented	O
in	O
a	O
straightforward	O
manner	O
.	O
</s>
<s>
)	O
,	O
each	O
of	O
the	O
aforementioned	O
statements	O
would	O
be	O
parallelized	B-Operating_System
for	O
simultaneous	O
execution	O
using	O
DOALL	O
parallelism	B-Operating_System
.	O
</s>
<s>
The	O
following	O
pseudocode	B-Language
illustrates	O
the	O
operation	O
of	O
DOACROSS	B-General_Concept
parallelism	I-General_Concept
in	O
such	O
a	O
situation	O
.	O
</s>
<s>
The	O
execution	O
time	O
of	O
DOACROSS	B-General_Concept
parallelism	I-General_Concept
largely	O
depends	O
on	O
what	O
fraction	O
of	O
the	O
program	O
suffers	O
from	O
loop-carried	O
dependence	O
.	O
</s>
<s>
DOACROSS	B-General_Concept
parallelism	I-General_Concept
suffers	O
from	O
significant	O
space	O
and	O
granularity	O
overheads	O
due	O
to	O
the	O
synchronization	O
primitives	O
used	O
.	O
</s>
