> -----Original Message-----
> From: Thomas Gleixner [mailto:t...@linutronix.de]
> Sent: Monday, May 18, 2015 10:18 PM
> To: Wu, Feng
> Cc: mi...@redhat.com; h...@zytor.com; linux-kernel@vger.kernel.org;
> jiang....@linux.intel.com
> Subject: Re: [v5 3/3] x86, irq: Define a global vector for VT-d
> Posted-Interrupts
>
> On Mon, 18 May 2015, Feng Wu wrote:
> > diff --git a/arch/x86/include/asm/hardirq.h b/arch/x86/include/asm/hardirq.h
> > index 0f5fb6b..9866065 100644
> > --- a/arch/x86/include/asm/hardirq.h
> > +++ b/arch/x86/include/asm/hardirq.h
> > @@ -14,6 +14,7 @@ typedef struct {
> > #endif
> > #ifdef CONFIG_HAVE_KVM
> > unsigned int kvm_posted_intr_ipis;
> > + unsigned int kvm_posted_intr_wakeup_ipis;
>
> So now we have another IPI with statistics and nothing which makes it
> accessible. kvm_posted_intr_ipis lacks a printout in
> arch_show_interrupts() as well.
>
I will add the printouts for these two IPIs.
> > #ifdef CONFIG_HAVE_KVM
> > +void (*wakeup_handler_callback)(void);
> > +EXPORT_SYMBOL_GPL(wakeup_handler_callback);
> > +
>
> The naming sucks. Which wakeup?
>
> As this is kvm specific, it should have a kvm_ prefix. And it should
> tell what it actually does:
>
> kvm_posted_intr_wakeup_handler
>
> Hmm?
Good suggestion!
>
> > /*
> > * Handler for POSTED_INTERRUPT_VECTOR.
> > */
> > @@ -256,6 +259,26 @@ __visible void smp_kvm_posted_intr_ipi(struct
> pt_regs *regs)
> >
> > set_irq_regs(old_regs);
> > }
> > +
> > +/*
> > + * Handler for POSTED_INTERRUPT_WAKEUP_VECTOR.
> > + */
> > +__visible void smp_kvm_posted_intr_wakeup_ipi(struct pt_regs *regs)
> > +{
> > + struct pt_regs *old_regs = set_irq_regs(regs);
> > +
> > + entering_ack_irq();
> > +
> > + inc_irq_stat(kvm_posted_intr_wakeup_ipis);
> > +
> > + if (wakeup_handler_callback)
> > + wakeup_handler_callback();
>
> Why do we need a conditional here?
>
> staic void dummy_handler(void) { }
> static void *kvm_posted_intr_wakeup_handler = dummy_handler;
>
> void kvm_set_posted_intr_wakeup_handler(void (*handler)(void))
> {
> if (handler)
> kvm_posted_intr_wakeup_handler = handler;
> else
> kvm_posted_intr_wakeup_handler = dummy_handler;
> }
>
> avoids the conditional in the exception handler....
Got it. Conditional branch in a critical path is really a bad thing...
Thanks,
Feng
>
> Thanks,
>
> tglx
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