linux-kernel - Re: [PATCH V7 07/14] perf/core: Add a new PERF_EV_CAP

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Message-ID: <20200724143258.GB10769@hirez.programming.kicks-ass.net>
Date:   Fri, 24 Jul 2020 16:32:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     acme@...hat.com, mingo@...nel.org, linux-kernel@...r.kernel.org,
        jolsa@...nel.org, eranian@...gle.com,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com,
        like.xu@...ux.intel.com
Subject: Re: [PATCH V7 07/14] perf/core: Add a new PERF_EV_CAP_COEXIST event
 capability

On Fri, Jul 24, 2020 at 10:19:25AM -0400, Liang, Kan wrote:
> There will be a problem for the current perf tool, which assumes that the
> leader event is the sampling event.
> 
> I will check how can we specially handle it in the perf tool.

Ah, okay. I've long lost track of how the tool works :/

Something that seems to 'work' is:
'{cycles,cpu/instructions,period=50000/}', so maybe you can make the
group modifier :S use any sampling event if there is one, and otherwise
designate the leader.

Then you can write things like:

  '{slots, metric1, metric2, cpu/cycles,freq=50000/}:S'

and then since cycles is specified as a sampling event, it will use
that.