Re: [PATCH v3 1/3] perfevent_pmda: Add extension for perf derived events

[Nathan Scott <nathans@xxxxxxxxxx>]

Hi Hemant,

----- Original Message -----
> This patch gives the ability to perfevent agent to monitor derived
> [...]

I've found one small issue with this just now - when we have no newly
derived metrics, we can see this...

$ pminfo -v perfevent
perfevent.derived: pmLookupDesc: Unknown or illegal metric identifier

I guess this is because there's nothing handling that (dynamic pmns)
node when no derived metrics are configured.

One solution might be to add a metric permanently below that point,
that is instantiated both with and without derived perfevent counts
e.g. perfevent.derived.active (mirror the existing perfevent.active)
- a count of #derived metrics - zero valued in the default case.

cheers.

--
Nathan