<s>
Fair-share	B-Operating_System
scheduling	I-Operating_System
is	O
a	O
scheduling	O
algorithm	O
for	O
computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
in	O
which	O
the	O
CPU	B-General_Concept
usage	O
is	O
equally	O
distributed	O
among	O
system	O
users	O
or	O
groups	O
,	O
as	O
opposed	O
to	O
equal	O
distribution	O
of	O
resources	O
among	O
processes	O
.	O
</s>
<s>
One	O
common	O
method	O
of	O
logically	O
implementing	O
the	O
fair-share	B-Operating_System
scheduling	I-Operating_System
strategy	O
is	O
to	O
recursively	O
apply	O
the	O
round-robin	B-Algorithm
scheduling	I-Algorithm
strategy	O
at	O
each	O
level	O
of	O
abstraction	O
(	O
processes	O
,	O
users	O
,	O
groups	O
,	O
etc	O
.	O
)	O
</s>
<s>
For	O
example	O
,	O
if	O
four	O
users	O
(	O
A	O
,	O
B	O
,	O
C	O
,	O
D	O
)	O
are	O
concurrently	O
executing	O
one	O
process	O
each	O
,	O
the	O
scheduler	O
will	O
logically	O
divide	O
the	O
available	O
CPU	B-General_Concept
cycles	O
such	O
that	O
each	O
user	O
gets	O
25%	O
of	O
the	O
whole	O
(	O
100%	O
/	O
4	O
=	O
25%	O
)	O
.	O
</s>
<s>
If	O
user	O
B	O
starts	O
a	O
second	O
process	O
,	O
each	O
user	O
will	O
still	O
receive	O
25%	O
of	O
the	O
total	O
cycles	O
,	O
but	O
each	O
of	O
user	O
B	O
's	O
processes	O
will	O
now	O
be	O
attributed	O
12.5	O
%	O
of	O
the	O
total	O
CPU	B-General_Concept
cycles	O
each	O
,	O
totalling	O
user	O
B	O
's	O
fair	O
share	O
of	O
25%	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
if	O
a	O
new	O
user	O
starts	O
a	O
process	O
on	O
the	O
system	O
,	O
the	O
scheduler	O
will	O
reapportion	O
the	O
available	O
CPU	B-General_Concept
cycles	O
such	O
that	O
each	O
user	O
gets	O
20%	O
of	O
the	O
whole	O
(	O
100%	O
/	O
5	O
=	O
20%	O
)	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
available	O
CPU	B-General_Concept
cycles	O
are	O
divided	O
first	O
among	O
the	O
groups	O
,	O
then	O
among	O
the	O
users	O
within	O
the	O
groups	O
,	O
and	O
then	O
among	O
the	O
processes	O
for	O
that	O
user	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
there	O
are	O
three	O
groups	O
(	O
1	O
,	O
2	O
,	O
3	O
)	O
containing	O
three	O
,	O
two	O
,	O
and	O
four	O
users	O
respectively	O
,	O
the	O
available	O
CPU	B-General_Concept
cycles	O
will	O
be	O
distributed	O
as	O
follows	O
:	O
</s>
