Hi Thomas,
On Wed, Nov 6, 2013 at 6:23 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>> Also note that the value of "nested" doesn't match the indentation level,
>> which depends on my own bookkeeping using "nesting".
>
> Well, nested is just an indicator. It's not the nest level.
I know, the only thing that matters is whether it's zero or not.
But it should always be zero if there's no nesting, and non-zero if there
is, right?
So:
# irq 13 nested 1024
nested should be 0 here.
# irq 4 nested 0
ok
# irq 13 nested 1024
ok (two extra spaces in front of "irq").
# irq 4 nested 0
nested should be non-zero here.
> nested = pt->sr & ~ALLOWINT;
> i.e.:
> nested = pt->sr & 0x0700;
>
> So in the case above nested is 0x400
>
>> Anyone with an idea where it's going wrong?
>
> The original code does:
>
> add_preempt_count(HARDIRQ_OFFSET);
>
> do_IRQ()
> irq_enter();
> add_preempt_count(HARDIRQ_OFFSET);
>
> handle_irq();
>
> irq_exit();
> local_irq_disable();
> sub_preempt_count(HARDIRQ_OFFSET);
>
> sub_preempt_count(HARDIRQ_OFFSET);
>
> /* Check for nested irq */
> if (in_hardirq())
> reti();
>
> /* Check for nested irq again */
> if (pt->sr & ~ALLOWINT != 0)
> reti();
>
> do_softirq();
> ....
> ret_from_exception();
>
> With the patches in place it looks like this:
>
> do_IRQ()
> nested = pt->sr & ~ALLOWINT;
>
> irq_enter();
> add_preempt_count(HARDIRQ_OFFSET);
>
> handle_irq();
>
> irq_exit_nested(nested);
> local_irq_disable();
> sub_preempt_count(HARDIRQ_OFFSET);
> if (!nested && !in_hardirq())
> do_softirq()
>
> return nested;
>
> if (nested)
> reti();
>
> ret_from_exception();
>
> So all it does essentially is to move the softirq invocation in the
> non nested case a tad earlier. I'm really puzzled as I can't spot the
> point where this change makes a real difference.
Yes, that's also my understanding.
But I can't spot it neither :-(
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
--
To unsubscribe from this list: send the line "unsubscribe linux-arch" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
