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

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Message-ID: <1277363069.3947.30.camel@yhuang-dev.sh.intel.com>
Date:	Thu, 24 Jun 2010 15:04:29 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, "H.PeterA" <"nvin hpa"@zytor.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC][PATCH] irq_work

On Thu, 2010-06-24 at 14:58 +0800, Peter Zijlstra wrote:
> On Thu, 2010-06-24 at 14:50 +0800, Huang Ying wrote:
> > On Thu, 2010-06-24 at 14:47 +0800, Peter Zijlstra wrote:
> > > On Thu, 2010-06-24 at 14:43 +0800, Huang Ying wrote:
> > > > Hi, Peter,
> > > 
> > > > I fact I uses exactly the similar method in my patches, just trigger it
> > > > with soft_irq instead of IRQ. Please take a look at
> > > > nmi_return_notifier_schedule in
> > > 
> > > But then why still use softirq? Once you have this its completely
> > > useless.
> > 
> > Some systems have no self interrupt, for example the system without
> > APIC. We need to provide a fallback for them. soft_irq can help here.
> 
> So there's systems that don't have self-ipi but do have NMI context?

Yes. NMI is there from 8259 age.

> Can't we run the callbacks from the tick or something for such legacy
> muck? I really don't like the whole softirq mess.

That is possible. But in NO_HZ system, we have no tick to rely on.
soft_irq is better here, because it will be triggered for any interrupt.

Best Regards,
Huang Ying

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