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

>
>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.

john
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