Re: [Xen-devel] System time monotonicity

[John Levon <levon@xxxxxxxxxxxxxxxxx>]

On Mon, Mar 26, 2007 at 07:59:27PM +0100, Keir Fraser wrote:

> On 26/3/07 19:50, "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxx> wrote:
> 
> > On your system it appears to be a couple of microseconds out, which is
> > on the high side of what we've observed. Normally you only see that kind
> > of mismatch on systems with TSCs running off different crystals.
> 
> More likely a jittery chipset timer -- we've observed less-than-ideal
> stability from some chipset timers, which can throw us off a bit when
> independently sync'ing the TSCs (which each CPU does for its TSC
> independently every couple of seconds).

And what about cross-VCPU monotonicity? It's called very frequently and
having to fake monotonicity via a single variable across all CPUs would
not be pleasant, unless I can think of something smarter...

regards
john

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