RE: [PATCH] i386: Selectable Frequency of the Timer Interrupt

["Maciej W. Rozycki" <macro@linux-mips.org>]

On Thu, 14 Jul 2005, Brown, Len wrote:

> >Of course using APIC internal timers is generally the best idea on SMP,
> >but they may have had reasons to avoid them (it's not an ISA interrupt,
> so
> >it could have been simply out of question in the initial design).
> 
> Best?  No.
> 
> Local APIC timers are based on a clock which on many processors will
> STOP when the processor enters power saving idle states, such as C3.
> So the LAPIC timer will not accurately reflect how much time
> has passed across entry/exit from idle.

 That's an APIC bug.  When Intel originally released the APIC (some 
thirteen years ago) they stated it should be used as a source of the timer 
interrupt instead of the 8254.  There is no excuse for changing the 
behaviour after so many years.  So if you are on a broken system, you may 
want to work around the bug, but it shouldn't impact good systems.

  Maciej
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