Re: [PATCH v2 05/12] x86/hvm: Remove duplicate calls caused by tracing

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.09.2021 19:25, Andrew Cooper wrote:
> 1) vpic_ack_pending_irq() calls vlapic_accept_pic_intr() twice, once in the
>    TRACE_2D() instantiation and once "for real".  Make the call only once.
> 
> 2) vlapic_accept_pic_intr() similarly calls __vlapic_accept_pic_intr() twice,
>    although this is more complicated to disentangle.
> 
>    v cannot be NULL because it has already been dereferenced in the function,
>    causing the ternary expression to always call __vlapic_accept_pic_intr().
>    However, the return expression of the function takes care to skip the call
>    if this vCPU isn't the PIC target.  As __vlapic_accept_pic_intr() is far
>    from trivial, make the TRACE_2D() semantics match the return semantics by
>    only calling __vlapic_accept_pic_intr() when the vCPU is the PIC target.
> 
> 3) hpet_set_timer() duplicates calls to hpet_tick_to_ns().  Pull the logic out
>    which simplifies both the TRACE and create_periodic_time() calls.
> 
> 4) lapic_rearm() makes multiple calls to vlapic_lvtt_period().  Pull it out
>    into a local variable.
> 
> vlapic_accept_pic_intr() is called on every VMEntry, so this is a reduction in
> VMEntry complexity across the board.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> --- a/xen/arch/x86/hvm/vpic.c
> +++ b/xen/arch/x86/hvm/vpic.c
> @@ -512,14 +512,15 @@ void vpic_irq_negative_edge(struct domain *d, int irq)
>  
>  int vpic_ack_pending_irq(struct vcpu *v)
>  {
> -    int irq;
> +    int irq, accept;

Strictly speaking "accept" wants to be bool, and ...

>      struct hvm_hw_vpic *vpic = &v->domain->arch.hvm.vpic[0];
>  
>      ASSERT(has_vpic(v->domain));
>  
> -    TRACE_2D(TRC_HVM_EMUL_PIC_PEND_IRQ_CALL, vlapic_accept_pic_intr(v),
> -             vpic->int_output);
> -    if ( !vlapic_accept_pic_intr(v) || !vpic->int_output )
> +    accept = vlapic_accept_pic_intr(v);

... vlapic_accept_pic_intr() would eventually also want to be
converted to return bool.

Jan