linux-kernel - Re: [PATCH v4 00/16] perf, persistent: Add persistent events

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Message-ID: <20140509091753.GT32718@rric.localhost>
Date:	Fri, 9 May 2014 11:17:53 +0200
From:	Robert Richter <rric@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Jean Pihet <jean.pihet@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>
Subject: Re: [PATCH v4 00/16] perf, persistent: Add persistent events

On 08.05.14 20:23:44, Borislav Petkov wrote:
> On Wed, May 07, 2014 at 06:44:07PM +0200, Robert Richter wrote:
> > With transparently I mean that the process even does not know that the
> > same event is already running by another process. The kernel detects
> > this and maps the request to that event and buffer. Of course the
> > event's buffer must be at least readonly to be shared for this.
> 
> Yes.
> 
> > This could be a mechanism to connect to persistent events. The kernel
> > detects by type and attr that the requested event is already running
> > persistent and maps to it.
> > 
> > But at the moment persistent events can only be shared using
> > 
> >  attr.type = PERF_TYPE_PERSISTENT
> >  attr.config = id
> > 
> > So the above is more an alternative to connect to persistent events
> > and the question is, which one to use. Presumable the easiest first,
> > which is the current implementation.
> 
> Well, there is no trivial way to share event buffers if they're not
> read-only AFAICT.
> 
> But in questions like this, we always have to step one step back and ask
> ourselves: what are the use cases for shared events and after we have
> enumerated them, to design the kernel side so that it supports them.
> 
> So, do we want anything else besides shared, read-only events?

I only talk about events that are sharable since they are read-only.

The question I am asking here is how to connect to an event that is
sharable. This could be done transparently.

-Robert
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