[dtrace-discuss] Inconsistent timestamps in DTrace output

Bryan Cantrill
Tue, 03 Jun 2008 17:21:21 -0000

Hey Andrew,

> We''re having problems with some of the timestamps produced by
dtrace
> where they seem to be roughly doubled (the following snippet is from the
> attached log file):
>
>
>
> 3037095639860141 on-cpu 1 4 59
>
> 3037095639864555 off-cpu 1
>
> 3037095649855777 on-cpu 1 4 59
>
> 3037095650461752 off-cpu 1
>
> 6074193317343753 on-cpu 1 1 59
>
> 6074193318047271 off-cpu 1
>
> 3037096589857081 on-cpu 1 4 59
>
> 3037096589861755 off-cpu 1
>
>
>
> The attached script file (''t'') was used to produce the
output and we
> used vmstat for the test. (> t vmstat )

This looks an awful lot like:

  6600939 gethrtime sometimes return a large time value into the future

This can have -- for arcane reasons -- symptoms that include the doubling
that you''re seeing.  This bug is fixed in Nevada (Build 77) and the fix
will also be in S10 Update 6...

	- Bryan

--------------------------------------------------------------------------
Bryan Cantrill, Sun Microsystems Fishworks.       http://blogs.sun.com/bmc