Messages in this thread | | | Date | 7 May 2009 14:07:32 -0400 | From | "George Spelvin" <> | Subject | Re: [RFC][PATCH] Adjust SHIFT_PLL to improve NTP convergence. |
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> IMHO, the "value" of calibration during boot is dubious (unless you just > reboot a "hot" machine): Usually the machine is cold on reboot, and the > oscillators will drift a lot initially. Depending on your environment, > the temperatures inside your box may rise about 10°C or more within a > few minutes.
> Maybe an experimental feature "recalibrate anytime (and as long as you'd > like)" would be interesting...
Well, a couple of points come to mind: - Rebooting hot is not all that unusual. Less so that with Windows, but some of us install test kernels from time to time. :-) - If you're calibrating the CPU against the PIT, they're often derived via PLL from the same clock source, so the *ratio* is fixed, and thus the calibration won't drift at all. - If there were some mechanism to make the divisor consistent across boots, that would be helpful. Imagine a file in /sys that I could write with an absolute frequency at boot time as long as it was within 1000 ppm (0.1%) of the kernel's measurement.
Thinking about it, the third option seems the most useful. It's basically a cleaned-up tickadj. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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