Negative ping times with FreeBSD 8.1-RELEASE on older Celeron system

Dan Nelson dnelson at
Wed Sep 14 18:10:51 UTC 2011

In the last episode (Sep 13), Brett Glass said:
> Thank you! Since it's tunable at runtime I just tested it, and -- sure
> enough -- no negative ping times.
> Ironically, it was the kernel that selected the ACPI timer, scoring it
> higher than the timestamp counter as a clock source.  Perhaps code should
> be added to ensure that the timer is not chosen if it rolls over in less
> than a second, since this clearly leads to imprecision and missed
> rollovers.
> 16777215                                    
> 7967112                                  
> 3579545                                
> 850       

It doesn't roll over in less than a second; it rolls over in 16777215 /
3579545 = 4.6 seconds.  Your negative time delta problem isn't due to

	Dan Nelson
	dnelson at

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