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

[George Anzinger <george@mvista.com>]

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