Messages in this thread | | | Date | Wed, 24 Apr 2002 19:25:39 +0200 (MET DST) | From | "Maciej W. Rozycki" <> | Subject | Re: Why HZ on i386 is 100 ? |
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On Tue, 23 Apr 2002, Andi Kleen wrote:
> That's the local APIC timer. Pretty much all modern x86 have it. > But at least microsoft warns from using them for high precision > tim ekeeping on their mmtimer page "due to inaccuracy and > frequent silicon bugs" (and I guess they have the data for that)
That's nothing new -- I recall a problem of missing half a tick each time when hardware reloads the timer after reaching zero with certain revisions of Pentium CPUs. It is documented in the specification update.
> The linux local APIC timer setup could be probably also improved, for > example the 16 multiplier is a bit dubious and the calibration does not > look very robust.
When fiddling with the predivider, please keep in mind the i82489DX only supports 2, 4, 8 and 16 as dividers and you may set up 1 (i.e. no division) but in a different way -- by setting LVTT appropriately (use SET_APIC_TIMER_BASE(APIC_TIMER_BASE_CLKIN)).
-- + Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: macro@ds2.pg.gda.pl, PGP key available +
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