Messages in this thread |  | | | Date | 8 May 2009 11:12:48 -0400 | | From | "George Spelvin" <> | | Subject | Re: [RFC][PATCH] tsc_khz= boot option to avoid TSC calibration variance |
| |
> Wouldnt it be a lot more flexible to have a sysctl for this, which > would be set before ntpd is started? (or which would be set by ntpd)
I thought so, but a boot-time option is sufficient and simpler.
> The mechanism and semantics would be similar: we would _not_ expose > cpu_khz directly, we'd have a boot_cpu_khz value saved for sure, and > we'd allow the sysctl to set the cpu_khz to within 1MHz of cpu_khz - > and we'd re-scale the timer irq and other calibrated values > accordingly.
Yes, that would be nicer.
> Alternatively, a much simpler method: why doesnt ntpd save its own > notion of cpu_khz once it has reached stability, and reads cpu_khz > (from /proc/cpuinfo) during bootup and re-scales its initial offset > and phase shift accordingly, compensating for that noise? (if it's > within 1MHz)
The problem is, it's only an issue if the TSC is used as the system time base, which is a kernel detail that a) NTP really doesn't want to be bothered with, and b) can change at run time.
It's possible, but it feels like a kludge. It's such a Linux-specific detail that it seems cleaner to fix it at the source.
|  |