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

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Message-ID: <1259617331.2076.146.camel@pasglop>
Date:	Tue, 01 Dec 2009 08:42:11 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Thomas Gleixner <tglx@...utronix.de>
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 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 ?

Cheers,
Ben.

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