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

[George Anzinger]

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@xxxxxxxxxx
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml

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