<s>
HiperDispatch	B-Application
is	O
a	O
workload	O
dispatching	O
feature	O
found	O
in	O
recent	O
IBM	B-Device
mainframe	I-Device
models	O
(	O
the	O
System	B-Device
z10	I-Device
and	O
IBM	O
zEnterprise	O
System	O
processors	O
and	O
later	O
models	O
)	O
running	O
recent	O
releases	O
of	O
z/OS	B-Application
.	O
</s>
<s>
HiperDispatch	B-Application
was	O
introduced	O
in	O
February	O
2008	O
.	O
</s>
<s>
Support	O
was	O
added	O
to	O
z/VM	B-Application
in	O
its	O
V6R3	O
release	O
on	O
July	O
26	O
,	O
2013	O
.	O
</s>
<s>
One	O
of	O
the	O
engineering	O
challenges	O
with	O
large	O
SMP	B-Operating_System
server	O
designs	O
is	O
to	O
maintain	O
near-linear	O
scalability	B-Architecture
as	O
the	O
number	O
of	O
CPUs	B-Device
increases	O
.	O
</s>
<s>
These	O
overhead	O
factors	O
become	O
increasingly	O
difficult	O
to	O
mitigate	O
as	O
the	O
number	O
of	O
CPUs	B-Device
increases	O
.	O
</s>
<s>
Each	O
new	O
mainframe	O
model	O
supports	O
a	O
higher	O
maximum	O
number	O
of	O
CPUs	B-Device
(	O
up	O
to	O
64	O
main	O
processors	O
in	O
a	O
single	O
System	B-Device
z10	I-Device
mainframe	O
for	O
example	O
)	O
,	O
so	O
this	O
engineering	O
challenge	O
becomes	O
ever	O
more	O
important	O
.	O
</s>
<s>
HiperDispatch	B-Application
helps	O
address	O
the	O
problem	O
through	O
a	O
combination	O
of	O
hardware	O
features	O
,	O
z/OS	B-Application
dispatching	O
,	O
and	O
the	O
z/OS	B-Application
Workload	B-Application
Manager	I-Application
.	O
</s>
<s>
In	O
z/OS	B-Application
there	O
may	O
be	O
tasks	O
waiting	O
for	O
processing	O
attention	O
,	O
such	O
as	O
transaction	O
programs	O
.	O
</s>
<s>
In	O
a	O
large	O
SMP	B-Operating_System
design	O
such	O
as	O
System	O
z	O
,	O
some	O
CPUs	B-Device
are	O
physically	O
"	O
closer	O
"	O
with	O
faster	O
access	O
to	O
cache	O
memory	O
that	O
might	O
hold	O
supporting	O
data	O
for	O
particular	O
tasks	O
.	O
</s>
<s>
HiperDispatch	B-Application
exploits	O
this	O
fact	O
and	O
steers	O
tasks	O
to	O
the	O
CPUs	B-Device
most	O
likely	O
to	O
have	O
the	O
fastest	O
access	O
to	O
relevant	O
data	O
already	O
in	O
cache	O
.	O
</s>
<s>
If	O
that	O
particular	O
CPU	B-Device
is	O
busy	O
,	O
HiperDispatch	B-Application
will	O
,	O
at	O
first	O
,	O
wait	O
for	O
it	O
to	O
finish	O
its	O
other	O
task	O
,	O
even	O
if	O
another	O
less	O
favorable	O
CPU	B-Device
is	O
idle	O
.	O
</s>
<s>
However	O
,	O
there	O
are	O
limitations	O
to	O
how	O
patient	O
HiperDispatch	B-Application
will	O
be	O
,	O
as	O
governed	O
by	O
Workload	B-Application
Manager	I-Application
goals	O
.	O
</s>
<s>
If	O
z/OS	B-Application
Workload	B-Application
Manager	I-Application
senses	O
that	O
there	O
's	O
a	O
risk	O
the	O
pending	O
task	O
will	O
miss	O
its	O
service	O
level	O
(	O
responding	O
within	O
a	O
certain	O
number	O
of	O
milliseconds	O
to	O
a	O
user	O
request	O
for	O
example	O
)	O
,	O
Workload	B-Application
Manager	I-Application
and	O
HiperDispatch	B-Application
will	O
send	O
the	O
task	O
over	O
to	O
an	O
idle	O
CPU	B-Device
for	O
processing	O
,	O
even	O
if	O
that	O
CPU	B-Device
must	O
fetch	O
data	O
from	O
slower	O
main	O
memory	O
.	O
</s>
<s>
HiperDispatch	B-Application
offers	O
very	O
little	O
CPU	B-Device
savings	O
benefit	O
on	O
machines	O
configured	O
with	O
a	O
relatively	O
small	O
number	O
of	O
CPUs	B-Device
.	O
</s>
<s>
However	O
,	O
the	O
feature	O
does	O
help	O
very	O
significantly	O
as	O
the	O
CPU	B-Device
count	O
increases	O
.	O
</s>
<s>
IBM	B-Device
mainframe	I-Device
capacity	O
tables	O
(	O
and	O
thus	O
its	O
software	O
pricing	O
)	O
are	O
all	O
based	O
on	O
the	O
assumption	O
that	O
HiperDispatch	B-Application
is	O
active	O
.	O
</s>
<s>
The	O
other	O
benefit	O
of	O
HiperDispatch	B-Application
-	O
"	O
parking	O
"	O
logical	O
CPUs	B-Device
so	O
that	O
the	O
number	O
of	O
CPUs	B-Device
on	O
which	O
z/OS	B-Application
dispatches	O
work	O
more	O
closely	O
matches	O
the	O
LPAR	B-Device
's	O
weight	O
-	O
is	O
applicable	O
to	O
even	O
small	O
machine	O
configurations	O
.	O
</s>
<s>
Workload	B-Application
Manager	I-Application
(	O
WLM	O
)	O
must	O
be	O
configured	O
correctly	O
for	O
HiperDispatch	B-Application
to	O
work	O
well	O
.	O
</s>
<s>
Some	O
mainframe	O
users	O
have	O
latent	O
problems	O
with	O
their	O
WLM	O
goal	O
settings	O
which	O
are	O
only	O
exposed	O
with	O
HiperDispatch	B-Application
,	O
so	O
there	O
is	O
an	O
option	O
to	O
disable	O
HiperDispatch	B-Application
in	O
those	O
cases	O
where	O
mainframe	O
users	O
do	O
not	O
want	O
to	O
correct	O
those	O
issues	O
right	O
away	O
.	O
</s>
<s>
However	O
,	O
regardless	O
of	O
whether	O
HiperDispatch	B-Application
is	O
on	O
or	O
off	O
,	O
it	O
's	O
important	O
for	O
installations	O
to	O
maintain	O
their	O
WLM	O
policy	O
.	O
</s>
<s>
To	O
configure	O
z/OS	B-Application
System	O
Resource	O
Manager	O
,	O
modify	O
Parmlib-Member	O
IEAOPTxx	O
:	O
</s>
<s>
YES	O
-	O
SRM	O
should	O
turn	O
on	O
HiperDispatch	B-Application
mode	O
.	O
</s>
<s>
NO	O
-	O
SRM	O
should	O
turn	O
off	O
HiperDispatch	B-Application
mode	O
.	O
</s>
<s>
Partitions	B-Device
with	O
more	O
than	O
64	O
logical	O
processors	O
at	O
IPL	O
time	O
are	O
forced	O
to	O
run	O
with	O
HIPERDISPATCH	B-Application
=	O
YES	O
.	O
</s>
<s>
After	O
IPL	O
,	O
LPARs	B-Device
with	O
more	O
than	O
64	O
logical	O
processors	O
cannot	O
switch	O
into	O
HIPERDISPATCH	B-Application
=	O
NO	O
.	O
</s>
<s>
In	O
case	O
of	O
HIPERDISPATCH	B-Application
=	O
YES	O
(	O
z196	O
and	O
follow-on	O
CPCs	O
)	O
,	O
IRD	B-Application
's	O
VARY	O
CPU	B-Device
management	O
is	O
automatically	O
turned	O
off	O
,	O
independent	O
of	O
the	O
"	O
VARYCPU	O
"	O
-specification	O
.	O
</s>
