linux-kernel - Re: Get rid of IRQF_DISABLED - (was [PATCH] genirq: warn about IRQF_SHARED|IRQF

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Date:	Mon, 30 Nov 2009 22:54:23 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Nicolas Pitre <nico@...vell.com>,
	Eric Miao <eric.y.miao@...il.com>,
	John Stultz <johnstul@...ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Remy Bohmer <linux@...mer.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrea Gallo <andrea.gallo@...ricsson.com>,
	Jamie Lokier <jamie@...reable.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Get rid of IRQF_DISABLED - (was [PATCH] genirq: warn about
 IRQF_SHARED|IRQF_DISABLED)

On Tue, 1 Dec 2009, Benjamin Herrenschmidt wrote:
> On Mon, 2009-11-30 at 22:31 +0100, Thomas Gleixner wrote:
> 
> > Are the perf events on power generally coming through the standard irq
> > handler code path and/or sensitive to local_irq_disable() ?
> 
> They are in HW yes. On ppc64, we do soft-disabling, which mean that we
> can still get the perf events within a local_irq_disable() region
> provided we don't get another interrupt within that region that forces
> us to hard disable so it would make the problem less bad I suppose.
> 
> > > I would suggest we timestamp the handlers in the core btw and warn
> > if
> > > they take too long so we get a chance to track down the bad guys.
> > 
> > The hassle is to find a time which we think is appropriate as a
> > threshold which is of course depending on the cpu power of a
> > system. Also I wonder whether we'd need to make such a warning thing
> > aware of irq nesting.
> 
> But if we always disable interrupts while running the handlers, we don't
> nest right ?

Right, in that case we do not and it's easy to instrument.

Thanks,

	tglx
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