Re: [Xen-devel] [PATCH for-4.13] x86/vmx: always sync PIR to IRR before vmentry

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.11.2019 12:03, Roger Pau Monné  wrote:
> On Wed, Nov 27, 2019 at 02:07:16AM +0000, Tian, Kevin wrote:
>> Then what's the difference from original logic?
> 
> The original logic is:
> 
> if ( running && (in_irq() || (v != current)) )
> {
>         unsigned int cpu = v->processor;
> 
>         if ( cpu != smp_processor_id() )
>             send_IPI_mask(cpumask_of(cpu), posted_intr_vector);
>         else if ( !softirq_pending(cpu) )
>             raise_softirq(VCPU_KICK_SOFTIRQ);
> }
> 
> Which I find much harder to understand. For example I'm not sure of
> what's the benefit of doing the cpu != smp_processor_id() check
> instead of simply doing v != current (like in the outer if condition).

There are two aspects to consider: One is that v->processor
may equal smp_processor_id() also for v != current. The other
is that without this check in the if() it would need adding
to the else-if(). I'm not sure to what degree which of the
two matters functionality wise.

Jan

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