Some newbie questions

[Avi Kivity]

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 well on my desktop, but very 
badly in production.