linux-kernel - Re: [RFC][PATCH] irq

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Date:	Thu, 24 Jun 2010 09:32:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "H.PeterA" <"nvin hpa"@zytor.com>,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC][PATCH] irq_work

On Thu, 2010-06-24 at 15:27 +0800, Huang Ying wrote:
> On Thu, 2010-06-24 at 15:19 +0800, Peter Zijlstra wrote:
> > On Thu, 2010-06-24 at 15:04 +0800, Huang Ying wrote:
> > 
> > > Yes. NMI is there from 8259 age.
> > 
> > But do we really care about such systems?
> > 
> > > That is possible. But in NO_HZ system, we have no tick to rely on.
> > 
> > Of course you have, you can delay the NO_HZ state when there's pending
> > callbacks, that's all of 1 line.
> > 
> > > soft_irq is better here, because it will be triggered for any interrupt.
> > 
> > Well, you can do the callbacks from irq_exit() as well, that's no
> > problem.
> 
> I think it is not a good idea to add overhead in such a hot path if the
> overhead can be avoided.

True, but I really don't like the softirq thing, and I really don't care
about !APIC machines, I probably couldn't buy one if I wanted to and its
not like we have good MCE support for them now, so who cares.
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