On Fri, Mar 09, 2007 at 07:24:42PM +0100, Benjamin Herrenschmidt wrote: > On Thu, 2007-03-08 at 16:04 +0100, Bram Senders wrote: > > Hi there, > > > > I am having issues with clock drift on my G4 Mac mini. The clock drifts > > so much that even ntpd can't keep up with it. I keep getting messages > > like "time reset +2.404131 s" from ntpd approximately every 15 to 20 > > minutes. > > I think the calibration OF puts in the device-tree is crap or we are > using the VIA to calibrate and we should not ... > > >From what I remember, Apple has additional calibration code in Darwin > based on the KeyLargo timers (for machines with a KeyLargo). Might be > worth implementing something similar. > > Look at pmac_calibrate_decr() in arch/powerpc/platform/powermac/time.c, > and see wether it's calling via_calibrate_decr() or not on your machine. > If not, try calling it and tell us if it improves calibration.
Okay, I did that. via_calibrate_decr() wasn't called, so I built a new kernel that called it anyway in the timer initialisation code, but this actually makes matters even worse. Grepping through my old kern.logs, I see that the decrementer frequency was always initialised either at 41.620907 MHz or 41.620997 MHz. I booted twice with the kernel that calls via_calibrate_decr() unconditionally; the first time the decrementer frequency was 40.639600 MHz, and 40.639583 Mhz the second time. I guess it is normal to have slightly differing frequencies here? Now I tried running ntpd, without having run tickadj or adjtimex, but this gives me very bad results: After having ntpd running for a few minutes, the offset is already something like -3000 ms, and the jitter is extremely large at about 2000 ms (which is less than 1 ms normally). Because of this large jitter, ntpd never gets the chance to synchronise to any server, and the offset gets progressively larger, to -35000 ms after less than an hour. The jitter has at this point doubled to approximately 4000 ms. During this period, I was randomly kicked out of my X session twice, which had never happened before, and hasn't happened since. I don't know how this could have anything to do with it, but it seems related. So, all in all, via_calibrate_decr() only makes things worse for me. If you know any other things to try, or need to know more, I'll be happy to try stuff out. Cheers, Bram -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
