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

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Date:	Thu, 11 Nov 2010 07:17:25 +0100
From:	Borislav Petkov <bp@...64.org>
To:	Ingo Molnar <mingo@...e.hu>
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>
Subject: Re: [PATCH 03/20] x86, mce: Add persistent MCE event

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.

In any case, we need some kind of a facility with which to export those
buffers for userspace to mmap. sysfs is clearly not that and debugfs is
what we currently use. I'm open for better suggestions though.

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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