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

From: Tony Lindgren (tony_at_atomide.com)
Date: 06/09/05

  • Next message: Lee Revell: "Re: [PATCH 3/4] new timeofday x86-64 arch specific changes (v. B1)" 
    Date:	Wed, 8 Jun 2005 18:40:33 -0700
To: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>

    * Pallipadi, Venkatesh <venkatesh.pallipadi@intel.com> [050608 15:14]:
    >
    > >-----Original Message-----
    > >From: linux-kernel-owner@vger.kernel.org
    > >[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of
    > >Jonathan Corbet
    > >Sent: Tuesday, June 07, 2005 1:36 PM
    > >To: Tony Lindgren
    > >Cc: linux-kernel@vger.kernel.org
    > >Subject: Re: [PATCH] Dynamic tick for x86 version 050602-1
    > >
    > >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.
    > >
    > >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.
    > >
    >
    > Good catch. This indeed looks like a bug.
    > With 050602-1 version I am seeing double the number of calls to
    > timer_interrupt routine than expected. Say, when all CPUs are fully
    > busy,
    > I see 2*HZ timer interrupt count in /proc/interrupts
    >
    > And things look normal once I change this hunk as below
    >
    > >> } 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);
    > + }

    Cool. Sorry for not responding earlier, my hard drive crashed yesterday
    morning... I also managed to fry my spare computer's motherboard
    while trying to recover some data from the broken disk :)

    I'll try to post an updated patch tomorrow.

    Tony
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