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Date: Wed, 8 Jul 2015 00:52:40 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>, Andi Kleen <ak@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        Jiri Olsa <jolsa@redhat.com>, Stephane Eranian <eranian@google.com>,
        mathieu.poirier@linaro.org, Pawel Moll <pawel.moll@arm.com>
Subject: Re: [PATCH V3 1/4] perf: Add PERF_RECORD_SWITCH to indicate context
 switches
Message-ID: <20150707225240.GW3644@twins.programming.kicks-ass.net>
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On Tue, Jul 07, 2015 at 01:13:59PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Jul 07, 2015 at 05:36:14PM +0200, Peter Zijlstra escreveu:
> > > To help userspace in places where all it has is the union perf_event, we
> > > can reuse one bit in misc to state that, i.e.
> 
> > >   #define PERF_RECORD_MISC_SWITCH_NEXT_PREV_PID 14
> 
> > > For instance.
> 
> > The other option would be a separate RECORD type, which might be
> > simpler.
> 
> Humm, do we really need it?
> 
> I think this is just us wanting to, since we are going to add a new
> record, to make it more useful for other, not right now needed,
> situations, i.e. if the user is priviledged, there are two other options
> to get his info, right?

I was just thinking that 2 records, each with a fixed layout would be
easier to parse than 1 record with variable layout.

The record space is immense, so from that point it really doesn't
matter.

Do whatever is easiest, less mistakes get made etc. :-)

No real preference either way, as long we we've thought about it.