Re: [RFC][PATCH] new timeofday core subsystem (v.A0)
From: George Anzinger
Date: Wed Sep 15 2004 - 13:03:38 EST
Dominik Brodowski wrote:
On Wed, Sep 15, 2004 at 01:04:04AM -0700, George Anzinger 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.
^^^^^^^^^^^^^^^^
On a largely idle system (like notebooks on battery power in typical use)
the accounting overhead will be less a problem. However, the CPU being
woken up each millisecond will cause an increased battery usage. So if
the load is less than a certain threshold, tickless systems do make much
sense.
At MontaVista I have been working on a thing we call VST which looks ahead in
the timer list and, finding nothing for N ticks, turns off the ticker until that
time. It is not tickless, unless the system is idle, but then it can go
tickless for as long as the max value that can be programmed on the wakeup
timer. Interrupts prior to that time will, of course, also wake the system.
Seems like the best of both worlds to me.
An early version of this is on the HRT sourceforge site.
--
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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