The main benefit is that with the default HZ=1000 nice +19 tasks now get 5
msecs of timeslices, so the ratio of CPU use is linear.  (nice 0 task gets
20 times more CPU time than a nice 19 task.  Prior this change the ratio
was 1:10)

another effect is that nice 0 tasks now get a round 100 msecs of timeslices
(as intended), instead of 102 msecs.

here's a table of old/new timeslice values, for HZ=1000 and 100:

                      HZ=1000         (   HZ=100   )
                    old    new        ( old    new )

        nice -20:   200    200        ( 200    200 )
        nice -19:   195    195        ( 190    190 )
        ...
        nice 0:     102    100        ( 100    100 )
        nice 1:      97     95        (  90     90 )
        nice 2:      92     90        (  90     90 )
        ...
        nice 17:     19     15        (  10     10 )
        nice 18:     14     10        (  10     10 )
        nice 19:     10      5        (  10     10 )

i've tested the patch on x86.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>