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Re: Proposed systemtap access to perfmon hardware


joshua wrote:

>  [...]
> > If they are started by default, where exactly are they running?
> > Beginning of begin probe? End of begin probe?
> 
> I think the perfmon setup needs to happen before all begin probes, so
> that the handle can be accessed within begin probes.  [...]

How important would that be?  At this time, we don't provide any
ordering guarantees amongst begin/end probes.  If a begin probe would
have to manipulate the handle, why not put that right into the
perfctr.*.setup probe directly?

> A side note about handles [...]  especially being able to
> dynamically enable/disable kprobes and timers.

Actual disarming of these kinds of probes is heavy-weight and may not
be safely done from within the confines of some generic
interrupt-disabled atomic probe handler.  For the perfctr case, we may
just directly poke at registers.

Programmatic control of swaths of probes is an interesting problem
though.


- FChE


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