Page 35 - slides.dvi

•
•
•
•
•
If
2.
3.
1.
In
to
Operating
For
Can
t n
we
For
where
history
be
τ n+1
Choose
=
Systems
come
τ 0
both
α,
general
—
=
0
Predicting
is
up
done
expand
an
≤
CPU
value
SJF
actual
α
by
of
with
the
some
irrelevant,
τ n+1
and
≤
α
Burst
1
Scheduling
predicted
=
length
EWMA
using
some
exponentially-weighted
is
of
SRTF
αt n
choose
formula
a
the
value
define:
constant.
+
way
α
n th
.
we
according
.
for
to
≈
Lengths
.
moving
good
to
1
require
+
length
get:
CPU
next
τ n+1
(1
of
our
the
and
predict
=
−
average
CPU
burst.
it.
predictor
next
then
belief
αt n
if
+
previous
get
burst.
the
(1
α) j αt n−j
about
“burst
−
CPU
(EWMA):
+
τ n+1
.
the
.
≈
.
α)τ n
variance
+
length”
bursts
t n .
is
(1
to
for
system,
−
small.
e.g.
each
if
calculate
α) n+1 τ 0
we
an
process
⇒
believe
need
31