linux-kernel - Re: [Xen-devel] [PATCH 1/3] Add mcelog support for xen platform

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Message-ID: <20120423170327.GC22364@phenom.dumpdata.com>
Date:	Mon, 23 Apr 2012 13:03:27 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	"Liu, Jinsong" <jinsong.liu@...el.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...64.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 1/3] Add mcelog support for xen platform

On Mon, Apr 23, 2012 at 09:17:28AM -0700, H. Peter Anvin wrote:
> On 04/23/2012 08:27 AM, Luck, Tony wrote:
> >> Because, if you'd hooked into it, just imagine one fine day, when we
> >> remove mcelog support, what screaming the xen people will be doing when
> >> mcelog doesn't work anymore.
> > 
> > Agreed. Even before we get to deleting mcelog, "struct mce" can change (new
> > fields could be added) ... and you don't want to have your hypervisor to
> > have to know which version of Linux it is talking to.
> 
> This is a great example on the fundamental problem with Xen, or rather
> the approach that Xen has taken of grabbing random kernel internals and
> claiming them as APIs (or, in some cases even as ABIs.)  A lot of these

I am _not_ claiming that. If I left you with that impression from my
responses - my fault for not getting my point across (the sleep deprevation
is probably not helping either).

I am _not_ stating that the usage of 'mce_log' or 'struct mce' MUST
remain the same from now on. No. I am saying that the driver will be
changed lock-step as Tony and Boris see fit in changing the functions.

And currently the way the existing MCE drivers do this - is by using
mce_log. This driver does is too - since the in-tree drivers do it this way.
When they change to use a different mechanism - this driver will as well.

> have had problems that are now very nearly unfixable, and that has
> seriously stalled out the ability of evolve the Linux kernel in some
> areas.  Note that the cost of this is borne by the development
> community, not by the Xen maintainers.

The ones I know that you are unhappy about are the MMU paravirt interfaces
and I did mention to you that once some prototype work is done and
it showed success, I will work on removing said support.

Why don't you send me your unhappy list so that is on my radar as well please?

> 
> 	-hpa
> 
> -- 
> H. Peter Anvin, Intel Open Source Technology Center
> I work for Intel.  I don't speak on their behalf.
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xen.org
> http://lists.xen.org/xen-devel
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