RE: [Xen-devel] [PATCH] Disable Xen PowerNow! support on Opteron 2nd gen and earlier processors

["Ian Pratt" <Ian.Pratt@xxxxxxxxxxxxx>]

> > Yes, and that is already done, hooked off the cpu notifier
> > callback chain.
> > Nobbling the C- and P-state logic shouldn't be necessary.
> 
> And yet, people are still reporting "Time went backwards"
> messages upwards of 30-40 times an hour on RevF Opterons
> when PowerNow! is enabled on Xen.
> 
> I spent a month trying to debug this and I made no significant
> progress.  If someone who understands Xen timekeeping wants to
> help me dive into this, I'll be glad to take another stab at
> it.  As it is, even with informing Xen of frequency changes,
> Xen does not ensure monotinicity.

I do think we need to understand what's going on here.

Are the 'time went backwards' messages correlated with power management
operations? How far is time stepping backwards? ns, us, or ms? 

Are you sure the systems aren't overheating and performing emergency
T-state thermal throttling?  

Ian





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