Re: CLOCK_MONOTONIC / CLOCK_UPTIME is not really monotonic between threads
Seo Townsend <[email protected]>
| Newsgroups | gmane.os.freebsd.devel.threading,gmane.os.freebsd.current,gmane.os.freebsd.questions,gmane.os.freebsd.architechture |
|---|---|
| Message-ID | <[email protected]> |
Heyy, Sure your machine isn’t sitting next to a block hole? :P Many of the names (CLOCK_XXXXXX) seem to be just aliased. https://github.com/freebsd/freebsd/blob/master/sys/kern/kern_time.c#L343 <https://github.com/freebsd/freebsd/blob/master/sys/kern/kern_time.c#L343> I didn’t thoroughly look at this, but it seems like there’s a margin of noise introduced by drift corrections that might (half ass-edly) explain the sub millisecond errors you were receiving? https://github.com/freebsd/freebsd/blob/master/sys/kern/kern_tc.c#L1374 <https://github.com/freebsd/freebsd/blob/master/sys/kern/kern_tc.c#L1347> For the larger >1ms errors, ...that’s probably not good? lol. Might be worth it to try the timersub library function: (http://www.unix.com/man-page/freebsd/3/timercmp/) to calculate the delta. > On Jun 3, 2016, at 7:28 AM, Maxim Sobolev <[email protected]> wrote: > > a. multiple cores. > b. makes no difference > c. yes, I believe so > > kern.timecounter.tsc_shift: 1 > kern.timecounter.smp_tsc_adjust: 0 > kern.timecounter.smp_tsc: 1 > kern.timecounter.invariant_tsc: 1 > machdep.tsc_freq: 2658118740 > machdep.disable_tsc_calibration: 0 > machdep.disable_tsc: 0 > > d. no, single socket Intel Q6700. I've also seen this problem on core > i7-4770 running virtualbox 5.x. I have a hints that this also happens on > our bigger production boxes, but I have no specifics yet. > > On Thu, Jun 2, 2016 at 10:05 PM, Adrian Chadd <[email protected]> > wrote: > >> [snip] >> >> a) is it on one core, or multiple cores? >> b) CLOCK_MONOTONIC_FAST? >> c) is it on a system that /has/ invariant-TSC ? >> d) is this a multi-socket system? >> >> >> >> -adrian >> >> > _______________________________________________ > [email protected] mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to "[email protected]" _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-threads To unsubscribe, send any mail to "[email protected]"