[dtrace-discuss] libdtrace and xcalls

[Bryan Cantrill]

> I've got an app that periodically runs dtrace scripts through libdtrace 
> and am seeing a good amount of xcalls from that.
> 
> I understand why dtrace uses xcalls, so this is an expected behavior to 
> a certain extent. But because my app repeats the scripts on an interval 
> basis, the amount of xcalls is higher than I'd like it to be.
> 
> Is there anything I can do to reduce that ?

Yes:  you can slow down your various rates (switchrate, aggrate, etc.)
But the xcalls are probably more cosmetic than an actual problem:  DTrace's
xcalls execute very quickly, and are unlikely to be causing system-wide
degradation.  (This is true of essentially all xcalls -- xcalls are more
likely to be a symptom of a larger problem than a problem in and of
themselves.)  Which raises a question:  how many xcalls are you seeing,
and have you used DTrace to make sure that they're all coming from DTrace?

	- Bryan

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