[Xen-devel] "Time went backwards" messages

[Don Fry <brazilnut@xxxxxxxxxx>]

I have a high end IBM system with 4 HT CPUs, am running xen-unstable
with only Dom0 active, and I get lots of "Timer ISR/n: Time went
backwards" messages.  This is a short segment from dmesg:

Timer ISR/1: Time went backwards: -259000 4465110000000 9741000 4465120000000
Timer ISR/6: Time went backwards: -224000 4465110000000 9776000 4465120000000
Timer ISR/6: Time went backwards: -159000 4465110000000 9841000 4465120000000
Timer ISR/3: Time went backwards: -145000 4465110000000 9856000 4465120000000
Timer ISR/1: Time went backwards: -161000 4465110000000 9839000 4465120000000
Timer ISR/1: Time went backwards: -51000 4465110000000 9950000 4465120000000
Timer ISR/6: Time went backwards: -25000 4465110000000 9976000 4465120000000
Timer ISR/3: Time went backwards: -40000 4465110000000 9961000 4465120000000
Timer ISR/7: Time went backwards: -9951000 4469140000000 49000 4469150000000
Timer ISR/2: Time went backwards: -9944000 4470150000000 56000 4470160000000
Timer ISR/6: Time went backwards: -9953000 4470550000000 47000 4470560000000
Timer ISR/5: Time went backwards: -9951000 4474600000000 49000 4474610000000

I looked at the archives and noticed this was reported when running
under VMware, but I see this happening with only xen and dom0.

The system has a Cyclone timer, and I am looking at using the Cyclone
timer to avoid the TSC drift, but while it is easy to add to xen, all
the cyclone support has been removed from linux.  

Are there any plans to restore Cyclone or HPET support to linux, and add
it to xen, to eliminate this kind of problem?

I have some prototype cyclone code added to xen, but have not done
anything to Linux yet.

-- 
Don Fry
brazilnut@xxxxxxxxxx

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