linux-kernel - Re: [PATCH 03/20] x86, mce: Add persistent MCE event

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Date:	Thu, 11 Nov 2010 09:58:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Borislav Petkov <bp@...64.org>
Cc:	Ben Gamari <bgamari@...il.com>,
	"acme@...radead.org" <acme@...radead.org>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 03/20] x86, mce: Add persistent MCE event


* Borislav Petkov <bp@...64.org> wrote:

> On Wed, Nov 10, 2010 at 05:21:57PM -0500, Ingo Molnar wrote:
> > 
> > * Ben Gamari <bgamari@...il.com> wrote:
> > 
> > > On Thu,  4 Nov 2010 16:36:39 +0100, Borislav Petkov <bp@...64.org> wrote:
> > > > From: Borislav Petkov <borislav.petkov@....com>
> > > > 
> > > > Add the necessary glue to enable the mce_record tracepoint on boot
> > > > turning it into a persistent event. This exports the MCE buffer
> > > > read-only to a userspace daemon which will hook into it through debugfs
> > > > when booting is finished.
> > > 
> > > While MCE technically is a diagnostics service, do we want to start adding 
> > > dependencies on debugfs in long-running, common-place daemons? I was under the 
> > > impression we were to avoid using debugfs for anything other than values for 
> > > one-off debugging.
> > 
> > See this current discussion thread on lkml:
> > 
> >    [RFC][PATCH] perf: sysfs type id
> > 
> > Events are being added to sysfs as we want to avoid the debugfs dependency.
> 
> Yep, event enumeration will land in /sysfs eventually but in this case debugfs is 
> used to export the buffers with the events recorded so far to the daemon which 
> mmaps them. And I remember also being mentioned that debugfs will thus be always 
> compiled in because of that.

The event ring-buffer can be mmap()-ed off the fd that sys_perf_event_open() gives. 
This is what all of tools/perf/ does - it uses debugfs only for even enumeration 
(which will move to sysfs).

Thanks,

	Ingo
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