Re: [Xen-devel] [v3 12/15] vmx: posted-interrupt handling when vCPU is blocked

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Tuesday, June 30, 2015 6:12 PM
> To: Wu, Feng; xen-devel@xxxxxxxxxxxxx
> Cc: keir@xxxxxxx; jbeulich@xxxxxxxx; Tian, Kevin; Zhang, Yang Z;
> george.dunlap@xxxxxxxxxxxxx
> Subject: Re: [v3 12/15] vmx: posted-interrupt handling when vCPU is blocked
> 
> On 24/06/15 06:18, Feng Wu wrote:
> > @@ -1848,6 +1869,33 @@ static struct hvm_function_table __initdata
> vmx_function_table = {
> >      .enable_msr_exit_interception = vmx_enable_msr_exit_interception,
> >  };
> >
> > +/*
> > + * Handle VT-d posted-interrupt when VCPU is blocked.
> > + */
> > +static void pi_wakeup_interrupt(struct cpu_user_regs *regs)
> > +{
> > +    struct arch_vmx_struct *vmx;
> > +    unsigned int cpu = smp_processor_id();
> > +
> > +    spin_lock(&per_cpu(pi_blocked_vcpu_lock, cpu));
> > +
> > +    /*
> > +     * FIXME: The length of the list depends on how many
> > +     * vCPU is current blocked on this specific pCPU.
> > +     * This may hurt the interrupt latency if the list
> > +     * grows to too many entries.
> > +     */
> > +    list_for_each_entry(vmx, &per_cpu(pi_blocked_vcpu, cpu),
> > +                        pi_blocked_vcpu_list)
> > +        if ( vmx->pi_desc.on )
> > +            tasklet_schedule(&vmx->pi_vcpu_wakeup_tasklet);
> 
> There is a logical bug here.  If we have two NV's delivered to this
> pcpu, we will kick the first vcpu twice.
> 
> On finding desc.on, a kick should be scheduled, then the vcpu removed
> from this list.  

So removing the vCPU from the blocking list here can avoid kicking the
vCPU multiple times, right?

Thanks,
Feng

With desc.on set, we know for certain that another NV
> will not arrive for it until it has been scheduled again and the
> interrupt posted.
> 
> ~Andrew
> 
> > +
> > +    spin_unlock(&per_cpu(pi_blocked_vcpu_lock, cpu));
> > +
> > +    ack_APIC_irq();
> > +    this_cpu(irq_count)++;
> > +}
> > +
> >  const struct hvm_function_table * __init start_vmx(void)
> >  {
> >      set_in_cr4(X86_CR4_VMXE);
> >


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel