linux-kernel - Re: [PATCH] perf, tools, script: Allow adding and removing fields

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Date:   Fri, 09 Jun 2017 11:13:11 +0200
From:   Milian Wolff <milian.wolff@...b.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Andi Kleen <andi@...stfloor.org>, acme@...nel.org,
        jolsa@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf, tools, script: Allow adding and removing fields

On Freitag, 9. Juni 2017 04:52:43 CEST Andi Kleen wrote:
> On Thu, Jun 08, 2017 at 02:59:58PM +0200, Milian Wolff wrote:
> > But I notice that this functionality is missing in other places too. Most
> > notably, I would like to be able to configure `perf stat` in a similar
> > way.
> > Such that one could do:
> > 
> > perf stat -e +cache-misses
> > 
> > Instead of
> > 
> > perf stat -e <whatever the defaults are>,cache-misses
> 
> The defaults are not great, so I'm not sure that is super useful.
> 
> It's probably better to assemble reasonable groups, perhaps
> with groups of metrics.
> 
> > But I cannot do:
> > 
> > $ perf record -e "topdown-*" ls
> > event syntax error: 'topdown-*'
> 
> That's actually good because the current topdown events are not useful to
> sample

Can you elaborate? I assume it's because you actually want to sample on 
instructions, and then group it together with the topdown events and 
potentially other counters like instructions?

> Usually you need to have at least some idea about the events you're
> collecting, and also for non trivial collections you need groups to get
> good results.

Yes, sure. But replace `record` with `stat` in the above and my point still 
stands.

> I've been thinking about adding MetricGroups to the json files, that
> would allow to assemble reasonable groups. But it still wouldn't be
> wildcard.
> 
> For a few things wildcards are useful, e.g. I implemented it recently
> for PMUs so that uncore PMUs are easier to handle.

I just noticed that I can actually use wildcards for tracepoints:

perf trace --no-syscalls --event "ext4:*"

And I think the same should be doable for PMU events with perf stat, but 
currently isn't:

$ perf stat -e "topdown*" ls
invalid or unsupported event: 'topdown*'
$ perf stat -e "branch*" ls
invalid or unsupported event: 'branch*'
$ perf stat -e "cache*" ls
invalid or unsupported event: 'cache*'

Bye

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