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    SubjectRe: [PATCH] x86: Don't ack_APIC_irq() if lapic is disabled in GENERIC_INTERRUPT_VECTOR handler
    [Ingo Molnar - Sun, Sep 20, 2009 at 08:21:24PM +0200]
    |
    | * Cyrill Gorcunov <gorcunov@gmail.com> wrote:
    |
    | > [Ingo Molnar - Sun, Sep 20, 2009 at 08:06:32PM +0200]
    | > |
    | > | * Sheng Yang <sheng@linux.intel.com> wrote:
    | > |
    | > | > Otherwise would cause trouble...
    | > | >
    | > | > Cc: Dimitri Sivanich <sivanich@sgi.com>
    | > | > Signed-off-by: Sheng Yang <sheng@linux.intel.com>
    | > | > ---
    | > | > arch/x86/kernel/irq.c | 3 ++-
    | > | > 1 files changed, 2 insertions(+), 1 deletions(-)
    | > | >
    | > | > diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
    | > | > index b0cdde6..78b23d0 100644
    | > | > --- a/arch/x86/kernel/irq.c
    | > | > +++ b/arch/x86/kernel/irq.c
    | > | > @@ -257,7 +257,8 @@ void smp_generic_interrupt(struct pt_regs *regs)
    | > | > {
    | > | > struct pt_regs *old_regs = set_irq_regs(regs);
    | > | >
    | > | > - ack_APIC_irq();
    | > | > + if (!disable_apic)
    | > | > + ack_APIC_irq();
    | > |
    | > | Wont in that case the apic->ack method be a NOP?
    | > |
    | > | Ingo
    | > |
    | >
    | > iirc it was Xen related patch. So it's not that simple.
    | >
    | > I've pointed out Sheng about disable_apic. I'm not Xen
    | > specialist but Xen team seem to use specific apic setup
    | > so our "dummy" operations are not involved (case they
    | > set disable_apic=1 without "turn off" apic ops in real).
    | > Something like that.
    |
    | They should then set a NOP function in that case. We really dont want to
    | slow down hotpath functions like smp_generic_interrupt() with flaggery.
    |
    | Ingo
    |

    Well, I suppose we should wait for Sheng's comments.
    I wish I would answer you but I simply don't know Xen
    code :)

    -- Cyrill


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