Re: [patch 0/2] Run interrupt handlers always with interrupts disabled

Ingo Molnar
2010-03-26T10:54:48Z

* 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