linux-kernel - Re: [PATCH 1/2] perf: Add persistent event facilities

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Date:	Fri, 18 May 2012 16:37:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <borislav.petkov@....com>
Subject: Re: [PATCH 1/2] perf: Add persistent event facilities

On Fri, 2012-05-18 at 16:21 +0200, Borislav Petkov wrote:
> On Fri, May 18, 2012 at 04:14:22PM +0200, Peter Zijlstra wrote:
> > On Fri, 2012-05-18 at 16:09 +0200, Borislav Petkov wrote:
> > > What happens here if a second user wants to enable a second set of
> > > persistent events, allocate a second set of per-CPU buffers? 
> > 
> > I'm not seeing the relation to VM_SHARED here.
> 
> Well, in the sense that if mmap fails in the !VM_SHARED case, I can't
> enable any persistent events except the ones which are enabled and so
> I need to allocate another set of resources for that second persistent
> events user.

Right, well, you could actually allow operations on the fd, just not a
second mapping :-)

Anyway.. I'd push that error back to the user. If they need a second
set, let them create it.

Do you really need multiple consumers for your MCE stuff? If so, what
would be the problem of using VM_SHARED?
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