Re: [RFC][PATCH] new timeofday core subsystem (v.A0)

George Anzinger
2004-09-15T18:05:17Z

Christoph Lameter wrote:
~

>>>One could do this but we want to have a tickless system. The tick is only
>>>necessary if the time needs to be adjusted.
>>
>>I really think a tickless system, for other than UML systems, is a loosing
>>thing. The accounting overhead on context switch (which increases as the number
>>of switchs per second) will cause more overhead than a periodic accounting tick
>>once a respectable load appears. The periodic accounting tick has a flat
>>overhead that does not depend on load.
>
>
> I am not following you here. Why does the context switch overhead
> increase? Because there are multiple interrupts for different tasks done
> in the tick?
>
Each task has several timers, i.e. time slice, time limit, and possibly itimer
profile. Granted only one of these needs to be sent to the timer code, but that
takes a bit of time, not much, but enough to increase the context switch
overhead such that a system with a modest amount of context switching will incur
more timer management overhead than the periodic tick generates.

--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml