On Wed, 2005-01-19 at 15:45 -0800, john stultz wrote: > On Thu, 2005-01-20 at 00:26 +0100, Thomas Gleixner wrote: > > On Wed, 2005-01-19 at 14:59 -0800, George Anzinger wrote: > > > I don't think you will ever get good time if you EVER reprogramm the PIT. > > > > Why not ? If you have a continous time source, which keeps track of > > "ticks" regardless the CPU state, why should PIT reprogramming be evil ? > > That's a big if. The problem is that while the PIT has its problems > (such as lost ticks), it runs at a known frequency and is reasonably > accurate. Time sources like the TSC have the problem that it doesn't run > at a known frequency, and thus we have to calibrate it (usually using > the PIT). Unfortunately this calibration is not extremely accurate > (George can go on to the reasons why), which causes the TSC to be a poor > stand alone time source. > > That said, the PIT is a poor time source as well, as it does loose ticks > and is very slow to access. ACPI PM and HPET are better as they don't > have the lost tick problem, but they are still off chip and slower to > access then the TSC.
And they aren't available on every board - especially not on embedded ones. > For an example of your ideal continuous timesource, check out the > timebase on PPC/PPC64. Other arches also have similar well behaved time > hardware. Yes, I'm aware of that. Unfortunately we live in the x86 universe. tglx - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
