Red Hat Bugzilla – Bug 589963
Time jump backwards in Guest r3u9-32
Last modified: 2013-01-10 21:58:44 EST
Created attachment 412325 [details]
Created attachment 412326 [details]
result of r3u9-32
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release. Product Management has requested further
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Please provide the qemu cmdline parameters and kvm/kernel versions.
Note that in 3.9 there is no pvclock, it's probably only the PIT.
Do you run anything special in the guest? NTP? Do any action like migration?
I find it pretty weird that the time goes backward for standard run.
Well, my 3.9 guest was using HPET, but that wasn't RHEL5. Since you're disabling HPET in the command line, the guest should probably end up using the dreaded TSC.
Can you strip -no-hpet from the options? I'm not sure if we officially support HPET for RHEL5, but the choice here is either fix the TSC or support the HPET.
hpet is not supported, I thought rhel3 uses the PIT, better add notsc cmdline to it
So that's PIT timer jumping backwards? Yikes.
Actually, can you post results from:
dmesg | grep -i time
It would be nice to confirm the PIT is really being used. Very strange the jiffies clock would cause backwards time or be any different on SMP.
Are you sure there is no ntpd / ntpdate running?
This bug is too confused to really make sense of. There are multiple guests running different versions of RHEL mentioned. I'm hopefully that Glauber's fixes and fixes to the various tick compensation mechanisms have already successfully resolved this bug. In any case, local testing hasn't shown unstable time in r3u9 guests - and if it's TSC compensation which is causing the problem, there is already another open bug for that which is assigned to me.