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Re: Some newbie questions



On 08/10/2016 06:32 PM, Frank Ch. Eigler wrote:

Avi Kivity <avi@scylladb.com> writes:


[...]
I'm surprised this didn't come up before.  Trying to find out why a
function which is usually fast and very rarely slow seems to be a good
fit for systemtap.

Like this?
https://sourceware.org/systemtap/examples/#profiling/fntimes.stp
Yes. The problem is that if the function is called often (with a usual short running time), then systemtap will eat all of the cpu time spinning on an internal lock. 


Note though that such analysis probably cannot be performed based only
upon PC samples - or even backtrace samples.  We seem to require
trapping individual function entry/exit events.
That's why I tried systemtap. It worked will on my desktop, but very badly in production.
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