linux-kernel - Re: [PATCH 02/18] xen: hook io

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Message-ID: <20090511111904.GK4648@elte.hu>
Date:	Mon, 11 May 2009 13:19:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 02/18] xen: hook io_apic read/write operations


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

>> And on a higher level, i still dont see why you dont do the whole 
>> Xen thing under an irqchip. There should be no extra crappy 
>> checks in native code.
>
> Hm, every time you see this code, you always have this 
> quasi-Pavlovian response.

Yep, my reaction to ugly code is pretty predictable, and 
(hopefully!) repeatable. So calling it Pavlovian is an implicit 
(albeit, i suspect, unintended ;-) compliment.

> You say "use an irqchip".  I say:
>
>    * We already use irqchip
>    * but most of the interesting IO apic accesses (routing) are not
>      done via the irqchip interface
>    * so irqchip doesn't help

I dont see the problem. All APIs within Linux are kept minimalistic 
and are extended on the fly, on an on-demand basis.

> And then you don't reply.  And then you raise it again.
>
> I would *always* prefer to hook into an interface like irqchip 
> rather than gouge into the code, but I really think that irqchip 
> isn't that interface.  If you have a more specific suggestion or 
> proposal I'll happily follow it up, but repeating "you should use 
> an irqchip" isn't getting anywhere.

Well, my main task at this stage is to point out ugly code. I might 
be able to do research for you and come up with a plan for you, but 
that's really a courtesy in general and is not always possible for 
maintainers. You might argue "of all possible solutions this is the 
cleanest" but i havent seen you make that point.

	Ingo
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