linux-kernel - Re: [PATCH 2/2] x86_64 irq: Handle irqs pending in IRR during irq migration.

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Message-ID: <m1hctyr921.fsf@ebiederm.dsl.xmission.com>
Date:	Tue, 06 Feb 2007 19:33:10 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	"Lu, Yinghai" <yinghai.lu@....com>,
	Luigi Genoni <luigi.genoni@...elli.com>,
	Natalie Protasevich <protasnb@...il.com>,
	Andi Kleen <ak@...e.de>
Subject: Re: [PATCH 2/2] x86_64 irq:  Handle irqs pending in IRR during irq migration.

Ingo Molnar <mingo@...e.hu> writes:

> * Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
>> Ingo would it be reasonable to get a wait queue so I can wait for an 
>> irq that needs the delayed disable action to actually become masked?
>
> that might make sense, but what will do the wakeup - incidental IRQ 
> arriving on the new CPU? 

That is what I was thinking.

> Isnt that a bit risky - maybe the device wont 
> generate IRQs for a really long time.

Well this is in a user space context called from user space and it
exactly matches the semantics we have now.  If we make it an
interruptible sleep the user space process shouldn't block.

I guess the other thing to do is do it in a non-block fashion
and just call schedule_work from the interrupt context when the
irq is disabled.  For i386 with it's in kernel irq scheduler
that might be better.

I think the nasty case is probably what do we do when it is
the timer interrupt we are dealing with.

Hmm.  I think I should look up what the rules are for
calling local_irq_enable when in interrupt context.  That
might be another way to satisfy this problem.

If local irqs are enabled I don't have to worry about the irr
register.

You've got me brainstorming now.

Eric
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