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Re: [Fwd: Re: stap early exit]


Darren Hart <dvhltc@us.ibm.com> writes:

> [...]
>> - change the "flag[tid()] = 0" to "delete flag[tid()]"
>
> Good idea, done.  Now the tapset will just stop... no longer getting the
> cleanup_and_exit message.

The effect of this should be to reduce the possibility of an array
overflow.  Should an array overflow, an explicit error message is
supposed to be printed, so it should not be a mystery.

>> - try removing the print_backtrace() calls
> This makes it run considerable longer. [...]

OK.  This, and ...

>> - check whether any probes were skipped
> Yes, I've seen between 30 and 100 probes skipped.

... this makes it likely that the script global variable contention is
indeed what's responsible.  You might find this wiki article helpful:
http://sources.redhat.com/systemtap/wiki/TipSkippedProbesOptimization


>> - try bumping up buffer size

> How do I do that?  the -s option?  'man stap' didn't state the
> default for -s

Yeah, that oversight should be corrected.  "stap -h" should list it, but
also doesn't.

> what do you suggest I start with?

You could try something on the order of 8 or 16, but I now don't think
it will matter.

- FChE


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