On Fri, 8 Mar 2013, Till Straumann wrote:
> 1) I'm not sure adding the SPURIOUS_DEFERRED flag into
> threads_handled_last is OK - what happens if the atomic_t counter
> can hold more than 31 bits? In this case, when thread handlers
> increment the counter there is interference with the flag. If
> this is not harmful then it is at least ugly.
atomic_t is going to stay 32 bit otherwise we'll have more horrible
problems than that one.
> I'm not as familiar with the code as you are but wouldn't it be
> simpler to always defer spurious detection thus avoiding to have to
> keep track of the state (deferral active/inactive)? I.e., if any
> primary handler returns IRQ_HANDLED then we simply increment the
> counter. note_interrupt() could then always compare the previous
> count to the current count and if they are equal conclude that the
> interrupt was not handled:
Yeah, we could do it that way. Would probably be simpler.
> handle_irq_event_percpu()
> {
> ...
> if (!noirqdebug)
> note_interrupt(irq, desc, retval);
>
> if ( (retval & IRQ_HANDLED) )
> atomic_inc(&desc->threads_handled);
> }
>
> and in 'note_interrupt()'
>
> handled = atomic_read(&desc->threads_handled);
> if ( desc->threads_handled_last == handled ) {
> action_ret = IRQ_NONE;
> } else {
> action_ret = IRQ_HANDLED;
> desc->threads_handled_last = handled;
> }
>
> Either way - I'm not sure what deferral does to the part of the algorithm
> in note_interrupt() which deals with misrouted interrupts since the
> 'action_ret' that goes into try_misrouted_irq() is delayed by one interrupt
> cycle.
That should not matter much methinks, but I'll try what explodes on
one of my affected machines.
>
> 2) note_interrupt is also called from irq/chip.c:handle_nested_irq() and I
> believe
> this routine would also need to increment the 'threads_handled' counter
> rather
> than calling note_interrupt.
That's a different issue. The nested_irq handler is for interrupts
which are demultiplexed by a primary threaded handler. That interrupt
is never handled in hard interrupt context. It's always called from
the context of the demultiplxing thread.
Thanks,
tglx
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