[ntp:questions] Re: what is the typical linux kernel clock like?

Ulrich Windl Ulrich.Windl at RZ.Uni-Regensburg.DE
Tue Feb 14 08:40:45 UTC 2006


You ask: "what is the typical linux kernel clock like?"
I'd say: "Quite good, but how's your hardware?"

This is some monitoring for a not-yet-released patch set for Linux 2.6:
(This version has been compiled on Linux 2.6.4
 using glibc-2.3. Now running Linux 2.6.15.1PPSAPI)
PPS API capabilities are 0x10f3
assert 1120 time 1139767167.000402394 delta 1.000000030 jitter 1535064674
assert 1121 time 1139767168.000402457 delta 1.000000063 jitter 33
assert 1122 time 1139767169.000402521 delta 1.000000064 jitter 1
assert 1123 time 1139767170.000402586 delta 1.000000065 jitter 1
assert 1124 time 1139767171.000402635 delta 1.000000049 jitter -16
assert 1125 time 1139767172.000402667 delta 1.000000032 jitter -17
assert 1126 time 1139767173.000402684 delta 1.000000017 jitter -15
assert 1127 time 1139767174.000402688 delta 1.000000004 jitter -13
assert 1128 time 1139767175.000402684 delta 0.999999996 jitter -8
assert 1129 time 1139767176.000402676 delta 0.999999992 jitter -4
assert 1130 time 1139767177.000402668 delta 0.999999992 jitter 0
assert 1131 time 1139767178.000402660 delta 0.999999992 jitter 0
assert 1132 time 1139767179.000402654 delta 0.999999994 jitter 2
assert 1133 time 1139767180.000402650 delta 0.999999996 jitter 2
assert 1134 time 1139767181.000402648 delta 0.999999998 jitter 2
assert 1135 time 1139767182.000402648 delta 1.000000000 jitter 2
assert 1136 time 1139767183.000402648 delta 1.000000000 jitter 0
assert 1137 time 1139767184.000402649 delta 1.000000001 jitter 1
assert 1138 time 1139767185.000402650 delta 1.000000001 jitter 0
assert 1139 time 1139767186.000402651 delta 1.000000001 jitter 0

Admittedly, the machine was idle, but you were asking how the clock is. You
see the clock seems quite stable if the hardware can deal with the load.

Disclaimer: The numbers look so good that I'm afraid there must be a bug
somewhere ;-)

Regards,
Ulrich


tom.horsley at att.net (Thomas A. Horsley) writes:

> Just idle curiosity:
> 
> Does frequently dropped time of day clock interrupts still give the typical
> linux kernel time keeping fits (to pick an example, the kernel version
> shipped with redhat enterprise linux)?
> 
> Wasn't there some talk once of (on i86, anwyay) using something like the TSC
> register to interpolate the interval between time of day interrupts so you
> could get smooth time keeping even if you missed some interrupts? Has
> anything like that made it into commonly distributed linux kernels? How
> tricky does it get if the kernel also supports variable clock speeds for
> power saving? :-).
> --
> >>==>> The *Best* political site <URL:http://www.vote-smart.org/> >>==+
>       email: Tom.Horsley at worldnet.att.net icbm: Delray Beach, FL      |
> <URL:http://home.att.net/~Tom.Horsley> Free Software and Politics <<==+




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