Re: User defined metrics for perf stat?

[Milian Wolff <milian.wolff@kdab.com>]

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On Wednesday, February 3, 2016 3:11:57 PM CET Jiri Olsa wrote:
> On Wed, Feb 03, 2016 at 01:39:20PM +0100, Milian Wolff wrote:
> > On Tuesday, February 2, 2016 9:58:02 AM CET Jiri Olsa wrote:
> > > On Tue, Feb 02, 2016 at 12:33:51AM +0100, Andreas Hollmann wrote:
> > > > Thanks, this is what I was looking for!
> > > > 
> > > > Why was the formula language abandoned? To restricted?
> > > > It would be still useful for interval prints.
> > > 
> > > yea the python script interface is way more powerful
> > > then whatever we would come with
> > 
> > How does this compare to the ongoing eBPF effort? Will we be able to do
> > eBPF based in-kernel aggregation for perf stat in the future?
> 
> hum, not sure what you mean by that, however this is
> all user level scripting support to allow user defined
> metrics/ratios from perf counters, more info ine here:
>   http://marc.info/?l=linux-kernel&m=145207742329050&w=2

I have not used eBPF at all yet, only read about it. Brendan's recent blog 
series was quite educative in that regard. That said, maybe I've so far 
completly misunderstood it. My current assumptions are:

- eBPF can be programmed in a C dialect
- it can be used to aggregate data on the fly, without introducing the 
userspace overhead
- the latter is especially important when your input source is extremely 
large, but you are only interested in an aggregate

Due to that, I thought this applies to perf stat. A eBPF program could then 
aggregate e.g. cycles and instruction counts on the fly to a CPI value. I 
imagine that would be extremely cheap to do there, and only the final CPI 
value would need to be passed to userspace for evaluation.

Bye

-- 
Milian Wolff | milian.wolff@kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

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