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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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