<s>
Anticipatory	B-Application
scheduling	I-Application
is	O
an	O
algorithm	O
for	O
scheduling	O
hard	B-Device
disk	I-Device
input/output	B-General_Concept
(	O
I/O	B-General_Concept
scheduling	I-General_Concept
)	O
.	O
</s>
<s>
It	O
seeks	O
to	O
increase	O
the	O
efficiency	O
of	O
disk	O
utilization	O
by	O
"	O
anticipating	O
"	O
future	O
synchronous	B-Architecture
read	O
operations	O
.	O
</s>
<s>
"	O
Deceptive	O
idleness	O
"	O
is	O
a	O
situation	O
where	O
a	O
process	B-Operating_System
appears	O
to	O
be	O
finished	O
reading	O
from	O
the	O
disk	O
when	O
it	O
is	O
actually	O
processing	O
data	O
in	O
preparation	O
of	O
the	O
next	O
read	O
operation	O
.	O
</s>
<s>
This	O
will	O
cause	O
a	O
normal	O
work-conserving	B-General_Concept
I/O	I-General_Concept
scheduler	I-General_Concept
to	O
switch	O
to	O
servicing	O
I/O	B-General_Concept
from	O
an	O
unrelated	O
process	B-Operating_System
.	O
</s>
<s>
This	O
situation	O
is	O
detrimental	O
to	O
the	O
throughput	O
of	O
synchronous	B-Architecture
reads	O
,	O
as	O
it	O
degenerates	O
into	O
a	O
seeking	O
workload	O
.	O
</s>
<s>
Anticipatory	B-Application
scheduling	I-Application
overcomes	O
deceptive	O
idleness	O
by	O
pausing	O
for	O
a	O
short	O
time	O
(	O
a	O
few	O
milliseconds	O
)	O
after	O
a	O
read	O
operation	O
in	O
anticipation	O
of	O
another	O
close-by	O
read	O
requests	O
.	O
</s>
<s>
Anticipatory	B-Application
scheduling	I-Application
yields	O
significant	O
improvements	O
in	O
disk	O
utilization	O
for	O
some	O
workloads	O
.	O
</s>
<s>
In	O
some	O
situations	O
the	O
Apache	B-Application
web	I-Application
server	I-Application
may	O
achieve	O
up	O
to	O
71%	O
more	O
throughput	O
from	O
using	O
anticipatory	B-Application
scheduling	I-Application
.	O
</s>
<s>
The	O
Linux	B-Operating_System
anticipatory	O
scheduler	O
may	O
reduce	O
performance	O
on	O
disks	O
using	O
Tagged	O
Command	O
Queuing	O
(	O
TCQ	O
)	O
,	O
high	O
performance	O
disks	O
,	O
and	O
hardware	O
RAID	B-Architecture
arrays	I-Architecture
.	O
</s>
<s>
An	O
anticipatory	O
scheduler	O
(	O
AS	O
)	O
was	O
the	O
default	O
Linux	B-Operating_System
kernel	I-Operating_System
scheduler	O
between	O
2.6.0	O
and	O
2.6.18	O
,	O
by	O
which	O
time	O
it	O
was	O
replaced	O
by	O
the	O
CFQ	B-Application
scheduler	O
.	O
</s>
<s>
As	O
of	O
kernel	B-Operating_System
version	O
2.6.33	O
,	O
the	O
Anticipatory	O
scheduler	O
has	O
been	O
removed	O
from	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
The	O
reason	O
being	O
that	O
while	O
useful	O
,	O
the	O
scheduler	O
's	O
effects	O
could	O
be	O
achieved	O
through	O
tuned	O
use	O
of	O
other	O
schedulers	O
(	O
mostly	O
CFQ	B-Application
,	O
which	O
can	O
also	O
be	O
configured	O
to	O
idle	O
with	O
the	O
slice_idle	O
tunable	O
)	O
.	O
</s>
<s>
Since	O
the	O
anticipatory	O
scheduler	O
added	O
maintenance	O
overhead	O
while	O
not	O
improving	O
the	O
workload	O
coverage	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
it	O
was	O
deemed	O
redundant	O
.	O
</s>
