Subject: Re: Get rid of IRQF_DISABLED - (was [PATCH] genirq: warn about
 IRQF_SHARED|IRQF_DISABLED)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
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       LKML <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       David Brownell <dbrownell@users.sourceforge.net>,
       Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
       Nicolas Pitre <nico@marvell.com>, Eric Miao <eric.y.miao@gmail.com>,
       John Stultz <johnstul@us.ibm.com>,
       Rusty Russell <rusty@rustcorp.com.au>, Remy Bohmer <linux@bohmer.net>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>,
       Andrea Gallo <andrea.gallo@stericsson.com>,
       Jamie Lokier <jamie@shareable.org>,
       linux-arm-kernel@lists.infradead.org
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Date: Tue, 01 Dec 2009 08:42:11 +1100
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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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