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SubjectRe: Problem with the O(1) scheduler in 2.4.19
On Tue, 3 Sep 2002 12:28:18 +0200 (CEST), Ingo Molnar <>

>On Tue, 3 Sep 2002, Tobias Ringstrom wrote:
>> For the case of a game server, this means that when the CPU utilization
>> gets above 50% (roughly), it will switch from -5 to +5 in dynamic
>> priority in a few seconds and stay there until the CPU utilization drops
>> under 50%.
>> Is my analysis correct, and is this what we want?
>do you expect a task that uses up 50% CPU time over an extended period of
>time to be rated 'interactive'?
>we might make the '50%' rule to be '100% / nr_running_avg', so that if
>your task is the only one in the system then it gets rated interactive -
>but i suspect it will still be rated a CPU hog if it keeps trying to use
>up 50% of CPU time even during busier periods. I have tried the
>(1/nr_running) rule in earlier incarnations of the scheduler, and it didnt
>make much difference, but we obviously need a boundary case like yours to
>see the differences.
>> I tried that yesterday (without the O(1) scheduler), and it does wonders
>> for the in-game latency (i.e. ping). I suppose that the dynamic prio
>> will still be +5 at 70% CPU utilization even with a HZ of 1000 using the
>> O(1) scheduler. Why would it make a difference?
>(it could in theory make a difference in some rare cases, in which the
>frequency of sampling resonates with internal timings of the application -
>i asked for this only to make sure there are no interactions.)
It seems to me that this condition could arise for any server process
which is used by many interactive processes. Imagine 300 users and a
server process which needs 70% to do the work. This could be a
database server as well as the current game server.

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