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Date: Thu, 17 May 2007 10:59:12 -0700
From: Nate Lawson <nate@root.org>
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To: Peter Jeremy <peterjeremy@optushome.com.au>
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Cc: acpi@freebsd.org
Subject: Re: PowerTOP for FreeBSD ?
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Peter Jeremy wrote:
> On 2007-May-16 00:00:46 -0700, Nate Lawson <nate@root.org> wrote:
>> Normally timers tick every 1 us on FreeBSD.
> 
> Unless something has changed massively, tradtiionally, hardclock
> interrupts every 1msec and statclick interrupts at 128Hz (approx
> 8msec).
> 

Oops, yes it's every 1 ms (1/1000 sec).  I didn't bother mentioning stat
clock since it's derived from hardclock and that's the only one that
makes the CPU exit its idle state.

>>  Most interrupts are
>> serviced with no work to be performed, so it's just wasted computation.
> 
> Using the lapic timer is an excellent example of this.  By default it
> runs at 2000Hz to run hardclock() every 1msec and statclock() every
> 7.5 msec - just under 50% of the interrupts are completely wasted.
> 

Absolutely.

-- 
Nate