linux-kernel - Re: [PATCH 02/18] perf: Add persistent event facilities

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Date:	Tue, 26 Apr 2011 16:05:57 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...64.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tony Luck <tony.luck@...el.com>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	David Ahern <dsahern@...il.com>,
	EDAC devel <linux-edac@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/18] perf: Add persistent event facilities

On Tue, Apr 26, 2011 at 08:45:10AM -0400, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Sat, 2011-04-23 at 18:28 +0200, Borislav Petkov wrote:
> > > From: Borislav Petkov <borislav.petkov@....com>
> > > 
> > > Add a barebones implementation for registering persistent events with
> > > perf. For that, we don't destroy the buffers when they're unmapped and
> > > we map them read-only so that multiple agents can access them.
> > > 
> > > Signed-off-by: Borislav Petkov <borislav.petkov@....com>
> > > ---
> > >  include/linux/perf_event.h |   22 ++++++++++++++++-
> > >  kernel/events/Makefile     |    2 +-
> > >  kernel/events/core.c       |   30 ++++++++++++++++++----
> > >  kernel/events/persistent.c |   56 ++++++++++++++++++++++++++++++++++++++++++++
> > >  4 files changed, 102 insertions(+), 8 deletions(-)
> > >  create mode 100644 kernel/events/persistent.c
> > > 
> > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > > index ee9f1e7..37bfae1 100644
> > > --- a/include/linux/perf_event.h
> > > +++ b/include/linux/perf_event.h
> > > @@ -216,8 +216,9 @@ struct perf_event_attr {
> > >                                 precise_ip     :  2, /* skid constraint       */
> > >                                 mmap_data      :  1, /* non-exec mmap data    */
> > >                                 sample_id_all  :  1, /* sample_type all events */
> > > +                               persistent     :  1, /* event always on */
> > 
> > But how will you find it again?
> > 
> > Persistent yells filesystem to me, and while we didn't use relayfs for 
> > various reasons, I think we do need something like it at the current stage.
> 
> eventfs or sysfs?
> 
> We need VFS space for event hierarchy enumeration anyway (and move the current 
> debugfs bits there). Persistent events could show up in that hiearachy as well.

I think we talked about this already in conjunction with moving event
hierarchy to sysfs - there you can have a "persistent" node too so you
can find it.

Here's what we talked about then:

https://lkml.org/lkml/2010/11/11/10

this and the following messages.

-- 
Regards/Gruss,
Boris.

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