From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch 0/2] Run interrupt handlers always with interrupts
 disabled
Date: Fri, 26 Mar 2010 11:53:58 +0100
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Thomas Gleixner <tglx@linutronix.de>, Nicolas Pitre <nico@fluxnic.net>, Linus Torvalds <torvalds@osdl.org>, LKML <linux-kernel@vger.kernel.org>, linux-arch@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>, Andi Kleen <andi@firstfloor.org>, David Miller <davem@davemloft.net>, Greg Kroah-Hartman <gregkh@suse.de>, Arnaldo Carvalho de Melo <acme@redhat.com>, Russell King <rmk@arm.linux.org.uk>


* Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, 2010-03-26 at 09:59 +0000, Alan Cox wrote:
> > > As long as it's rare (which it is) i dont see a problem: you can enable 
> > > interrupts in the handler by using local_irq_enable(), like the IDE PIO 
> > > drivers do. That way it's documented a bit better as well, because it shows 
> > > the precise source of the latency, with a big comment explaining it, etc.
> > 
> > I don't think it's as rare as you think particularly in embedded, and the 
> > moment you start explicitly using local_irq_enable() you've simply moved 
> > the underlying problem back and made it far harder to grep for.
> 
> We've got local_irq_enable_in_hardirq() which should be used and can easily 
> be grep'ed for.
> 
> But yes, I would much prefer to simply convert these known slow handlers to 
> threaded interrupts.

Yeah, agreed. So there's multiple solutions:

 - On old hw with a driver that nobody is willing to convert to threaded IRQs: 
   use the existing local_irq_enable_in_hardirq() API. This preserves the 
   status quo.

 - On new hw with new drivers where there's such a level of IRQ parallelism 
   that enabling IRQs in hardirqs is not an option, use threaded IRQ handlers.

Thanks,

	Ingo