linux-kernel - Re: [PATCH RT] add pending in fasteoi for IOAPIC hack

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Date:	Wed, 12 Dec 2007 22:35:40 -0500
From:	Jon Masters <jcm@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RT] add pending in fasteoi for IOAPIC hack

On Wed, 2007-12-12 at 15:41 -0500, Steven Rostedt wrote:
> The IOAPIC hack that does a level=>edge to mask does not disable
> interrupts. So we can receive interrupts when masked, and this means
> that we can miss interrupts that arrive when the thread is handling
> them.
> 
> This patch adds the "IRQ_PENDING" logic of the edge irqs to be
> able to catch interrupts coming in when supposably "masked".

ACK on all of these. I've been using them internally for a bit in
pursuit of a later problem. Additionally, I am currently reworking the
level->edge->level hack because it's known to be in violation of a
number of errata from third parties. The "legacy mode" hack is actually
only need on certain systems, which have e.g. a PCIe host bridge with
integrated IO-APIC that snoops the APIC to determine mask status.

I'm going to add a blacklist and quirks instead, as doing
level->edge->level otherwise causes us to start losing interrupts on
other systems. I will supply more information later - this is a somewhat
involved problem that we (Red Hat) have been looking at for a while.

Jon.

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