linux-kernel - Re: PCI, ACPI, IRQ, IOAPIC: reroute PCI interrupt to legacy boot interrupt equivalent

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Message-Id: <1231806563.4094.25.camel@perihelion.bos.jonmasters.org>
Date:	Mon, 12 Jan 2009 19:29:23 -0500
From:	Jon Masters <jcm@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Bjorn Helgaas <bjorn.helgaas@...com>,
	Stefan Assmann <sassmann@...e.de>, Len Brown <lenb@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Olaf Dabrunz <od@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-acpi@...r.kernel.org, Sven Dietrich <sdietrich@...ell.com>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: PCI, ACPI, IRQ, IOAPIC: reroute PCI interrupt to legacy boot
	interrupt equivalent

On Mon, 2009-01-12 at 15:36 -0800, Eric W. Biederman wrote:

> This hardware behavior is not specific to boot interrupts or Intel.

It's not specific to Intel, but it is a specific compatibility behavior.

> Is this case really so interesting and compelling that we want to fight
> through and figure what we need to do to make this work reliably on every
> x86 chipset?

How else do you propose implementing IRQ handling in e.g. the RT kernel?
We get a hardware interrupt, we can't FastEOI, we can't process
synchronously, we can't do all of those things you might expect.
Implementing RT requires that we delay handling of the IRQ until
arbitrarily later in the future when we get around to it.

Jon.


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