Re: [PATCH] Dynamic tick for x86 version 050602-1

From: Tony Lindgren (tony_at_atomide.com)
Date: 06/10/05

  • Next message: Tony Lindgren: "[PATCH] Dynamic tick for x86 version 050609-2" 
    Date:	Thu, 9 Jun 2005 21:18:42 -0700
To: Jonathan Corbet <corbet@lwn.net>

    * Jonathan Corbet <corbet@lwn.net> [050607 13:36]:
    > Tony Lindgren <tony@atomide.com> wrote:
    >
    > > --- linux-dev.orig/arch/i386/kernel/irq.c 2005-06-01 17:51:36.000000000 -0700
    > > +++ linux-dev/arch/i386/kernel/irq.c 2005-06-01 17:54:32.000000000 -0700
    > > [...]
    > > @@ -102,6 +103,12 @@ fastcall unsigned int do_IRQ(struct pt_r
    > > );
    > > } else
    > > #endif
    > > +
    > > +#ifdef CONFIG_NO_IDLE_HZ
    > > + if (dyn_tick->state & (DYN_TICK_ENABLED | DYN_TICK_SKIPPING) && irq != 0)
    > > + dyn_tick->interrupt(irq, NULL, regs);
    > > +#endif
    > > +
    > > __do_IRQ(irq, regs);
    >
    > Forgive me if I'm being obtuse (again...), but this hunk doesn't look
    > like it would work well in the 4K stacks case. When 4K stacks are being
    > used, dyn_tick->interrupt() will only get called in the nested interrupt
    > case, when the interrupt stack is already in use. This change also
    > pushes the non-assembly __do_IRQ() call out of the else branch, meaning
    > that, when the switch is made to the interrupt stack (most of the time),
    > __do_IRQ() will be called twice for the same interrupt.

    Good catch as mentioned earlier :)

    > It looks to me like you want to put your #ifdef chunk *after* the call
    > to __do_IRQ(), unless you have some reason for needing it to happen
    > before the regular interrupt handler is invoked.

    Time needs to be updated before __do_IRQ() so interrupt handlers have
    correct time.

    Tony
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