Re: lockdep and threaded IRQs (was: ...)

Peter Zijlstra
2009-03-02T21:42:21Z

On Mon, 2009-03-02 at 13:37 -0800, David Brownell wrote:

> > How so?, its the natural extension of that work.
>
> Not the work to shrink the amount of time IRQ latencies
> by shrinking the amount of time IRQs are disabled by
> IRQ handlers.

Ugh, that's done by pushing work out of the hardirq context, not by
doing silly things like enabling irqs from hardirq context.

> > > > we should simply always disable interrupts for
> > > > interrupt handlers.
> > >
> > > That would be why you have refused to fix the bug
> > > in lockdep, whereby it forcibly enables that flag?
> > >
> > > I've been wondering for some months now why you've
> > > left that bug unfixed.
> >
> > Because running irq handlers with irqs enabled it plain silly.
>
> Not if you have hardware-prioritized IRQs, which are
> fairly common in some environments ... handling an IRQ
> for high priority device A needn't interfere with the
> handler for lower priority device B, and the system
> overall can work better.
>
> Not if you need to shrink IRQ latencies by minimizing
> irqs-off critical sections everywhere ... IRQ handlers
> being common offenders for keeping IRQs off too long.
>
> Not when IRQs can be disabled selectively around the
> real critical sections ... so drivers can leave IRQs
> enabled except in those brief sections.

Yeah, and who gets to debug the stack overflow?

Hardware with irq prio levels can do a prio mask and use a stack per
prio level.