Re: [XEN][PATCH] xen/evtchn: enable build optimization for evtchn_move_pirqs()/send_guest_pirq()

[Grygorii Strashko <grygorii_strashko@xxxxxxxx>]

On 17.07.25 18:33, Jan Beulich wrote:
> On 17.07.2025 16:41, Grygorii Strashko wrote:
> > On 17.07.25 16:10, Jan Beulich wrote:
> > > On 17.07.2025 15:01, Grygorii Strashko wrote:
> > > > --- a/xen/common/event_channel.c
> > > > +++ b/xen/common/event_channel.c
> > > > @@ -975,6 +975,9 @@ void send_guest_pirq(struct domain *d, const struct pirq 
> > > > *pirq)
> > > >        int port;
> > > >        struct evtchn *chn;
> > > >    
> > > > +    if (!IS_ENABLED(CONFIG_HAS_PIRQ))
> > > > +        return;
> > > > +
> > > >        /*
> > > >         * PV guests: It should not be possible to race with __evtchn_close(). 
> > > > The
> > > >         *     caller of this function must synchronise with pirq_guest_unbind().
> > > Isn't this function unreachable on Arm, and hence a Misra rule 2.1 violation,
> > > requiring #ifdef around the entire function to address?
> > Yes. It's unused on Arm, only x86 is an user.
> > I can put it under ifdef.
> >
> > > > @@ -1710,10 +1713,15 @@ void evtchn_destroy_final(struct domain *d)
> > > >    void evtchn_move_pirqs(struct vcpu *v)
> > > >    {
> > > >        struct domain *d = v->domain;
> > > > -    const cpumask_t *mask = cpumask_of(v->processor);
> > > > +    const cpumask_t *mask;
> > > This change shouldn't be necessary; compilers ought to be able to DCE the
> > > code.
> > Unfortunately not, with "-O1" more code is generated as cpumask_of() is 
> > complicated inside.
> >
> > > >        unsigned int port;
> > > >        struct evtchn *chn;
> > > >    
> > > > +    if (!IS_ENABLED(CONFIG_HAS_PIRQ))
> > > Nit (style): Missing blanks (see other nearby if()-s).
> > >
> > > I wonder though whether we wouldn't better have x86'es arch_move_irqs()
> > > invoke this function, and then #ifdef it out here altogether as well.
> > Do you mean as in the below diff?
> Along these lines, yes. I guess personally I wouldn't convert to an
> out-of-line function. If an inline function fails to compile (and that
> isn't easily fixable), use a macro instead.
I'd prefer stick to out-of-line function, if you don't mind.
Inline implementation causes cascade build failure:

adding
 #include <xen/event.h>
 #include <xen/sched.h>
in irq.h is not enough.

> > --- a/xen/arch/x86/include/asm/irq.h
> > +++ b/xen/arch/x86/include/asm/irq.h
> > @@ -224,7 +224,7 @@ void cleanup_domain_irq_mapping(struct domain *d);
> >    
> >    bool cpu_has_pending_apic_eoi(void);
> >    
> > -static inline void arch_move_irqs(struct vcpu *v) { }
> > +void arch_move_irqs(struct vcpu *v);
> >    
> >    struct msi_info;
> >    int allocate_and_map_gsi_pirq(struct domain *d, int index, int *pirq_p);
> > diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
> > index 556134f85aa0..b8d8f202119d 100644
> > --- a/xen/arch/x86/irq.c
> > +++ b/xen/arch/x86/irq.c
> > @@ -1851,6 +1851,10 @@ void pirq_guest_unbind(struct domain *d, struct pirq 
> > *pirq)
> >            cleanup_domain_irq_pirq(d, irq, pirq);
> >    }
> >    
> > +void arch_move_irqs(struct vcpu *v) {
> > +    evtchn_move_pirqs(v);
> > +}
> > +
> >    static bool pirq_guest_force_unbind(struct domain *d, struct pirq *pirq)
> >    {
> >        struct irq_desc *desc;
> > diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
> > index 13fdf57e57b9..ad6032fb2865 100644
> > --- a/xen/common/sched/core.c
> > +++ b/xen/common/sched/core.c
> > @@ -642,7 +642,6 @@ int sched_init_vcpu(struct vcpu *v)
> >    static void vcpu_move_irqs(struct vcpu *v)
> >    {
> >        arch_move_irqs(v);
> > -    evtchn_move_pirqs(v);
> >    }
--
Best regards,
-grygorii