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Re: cost of kprobe and jprobe operations


Frank Ch. Eigler wrote:
Hi -



[...]
These performance discussions might be more meaningful if we had explicit performance goals for systemtap. [...]
Any thoughts on defining performance goals for systemtap?


I don't think picking numbers does harm, but I don't know how
much good that does either.  Would we stop-ship a systemtap
implementation that didn't meet the goals?  In the abstract,
should one opt to optimize vs. extend functionality?  Maybe
these questions should be put aside until something runnable
exists as a point of reference, when actual decisions might
need to be made.


- FChE

I generated these number to give some concrete numbers on the cost of the operations. We do want to be aware of the costs of the operations. There are certainly going to be some points where instrumentation is going to cause excessive overhead.


There are other performance issues with kprobes. There is a single spinlock used by all kprobes and this is going to serialize the probes. This will have a impact on smp scalability.

-Will


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