Re: [Xen-devel] [PATCH] per-cpu timer changes

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 26 May 2005, at 18:34, Don Fry wrote:

> The time going backwards was only occasionally, and it was a BIG jump
> backwards.  I tracked it down yesterday to a problem with doing 32-bit
> arithmetic in Linux on the tsc values.  For some reason, every 5-20
> minutes xen seems to pause for about 5 seconds.  This causes the tsc to
> wrap if only 32-bits are used, and the 'time went backwards' message is
> printed.  I changed to use 64-bit tsc deltas and have been running 
> since
> yesterday afternoon without any 'time went backwards' messages.  I want
> to do some more cleanup (remove my debugging code) and will post all my
> changes to the list this afternoon.
It would be good to know where those 5 seconds go. Doing 64-bit 
arithmetic on x86 will be slower and possibly fudge over the underlying 
problem.
 -- Keir


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