Re: [PATCH] Minor scheduler fix to get rid of skipping in xmms

[Nick Piggin <piggin@cyberone.com.au>]

John Yau wrote:

>>Even if context switches don't cost anything, you still want to have
>>priorities so cpu hogs can be preempted by other tasks in order to
>>quickly respond to IO events. You want interactive tasks to be able
>>to sometimes get more cpu than cpu hogs, etc. Scheduling latency is
>>only a part of it.
>>
>>
>
>Of course priorities are still necessary =)  However assuming that
>interactive tasks will always finish much much earlier than hogs, it's not
>really worth it to give interactive tasks any special treatment when you
>have very fine timeslices.
>

Its actually more important when you have smaller timeslices, because
the interactive task is more likely to use all of its timeslice in a
burst of activity, then getting stuck behind all the cpu hogs.

>
>
>For example you have x that will use 100 ms and y that will use 5 ms, both
>of the same priority.  Assuming that x entered into the queue first and y
>immediately after, at 20 ms timeslice, it will be 25 ms before y finishes.
>However, at 1 ms timeslice, y finishes in 10 ms.
>
>

Yes. Also, say 5 hogs running, an interactive task needs to do something
taking 2ms. At a 2ms timeslice, it will take 2ms. At a 1ms timeslice it
will take 6ms.