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

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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