On Wed, Oct 09, 2019 at 10:37:38AM +0200, Greg Kurz wrote: > On Wed, 9 Oct 2019 17:08:18 +1100 > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > Traditional PCI INTx for vfio devices can only perform well if using > > an in-kernel irqchip. Therefore, vfio_intx_update() issues a warning > > if an in kernel irqchip is not available. > > Can you elaborate on what doesn't "perform well" without an > in-kernel irqchip ?
Not really, no, but Alex Williamson tells me it is soo.
> Is it a matter of performance or is it
> actually broken or something else ?
I believe it's a matter of performance, but such a big one that it
makes using it without kernel irqchip infeasible in many cases.
> What is the impact on -machine accel=kvm,kernel-irqchip=off which
> always spit this warning ?
It should still spit that warning.
> > We usually do have an in-kernel irqchip available for pseries machines
> > on POWER hosts. However, because the platform allows feature
> > negotiation of what interrupt controller model to use, we don't
> > currently initialize it until machine reset. vfio_intx_update() is
> > called (first) from vfio_realize() before that, so it can issue a
> > spurious warning, even if we will have an in kernel irqchip by the
> > time we need it.
> >
> > To workaround this, make a call to spapr_irq_update_active_intc() from
> > spapr_irq_init() which is called at machine realize time, before the
> > vfio realize. This call will be pretty much obsoleted by the later
> > call at reset time, but it serves to suppress the spurious warning
> > from VFIO.
> >
> > Cc: Alex Williamson <alex.william...@redhat.com>
> > Cc: Alexey Kardashevskiy <a...@ozlabs.ru>
> >
> > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
> > ---
> > hw/ppc/spapr_irq.c | 11 ++++++++++-
> > 1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/ppc/spapr_irq.c b/hw/ppc/spapr_irq.c
> > index 7964e4a1b8..3aeb523f3e 100644
> > --- a/hw/ppc/spapr_irq.c
> > +++ b/hw/ppc/spapr_irq.c
> > @@ -274,6 +274,14 @@ void spapr_irq_init(SpaprMachineState *spapr, Error
> > **errp)
> >
> > spapr->qirqs = qemu_allocate_irqs(spapr_set_irq, spapr,
> > smc->nr_xirqs + SPAPR_XIRQ_BASE);
> > +
> > + /*
> > + * Mostly we don't actually need this until reset, except that not
> > + * having this set up can cause VFIO devices to issue a
> > + * false-positive warning during realize(), because they don't yet
> > + * have an in-kernel irq chip.
> > + */
> > + spapr_irq_update_active_intc(spapr);
> > }
> >
> > int spapr_irq_claim(SpaprMachineState *spapr, int irq, bool lsi, Error
> > **errp)
> > @@ -429,7 +437,8 @@ void spapr_irq_update_active_intc(SpaprMachineState
> > *spapr)
> > * this.
> > */
> > new_intc = SPAPR_INTC(spapr->xive);
> > - } else if (spapr_ovec_test(spapr->ov5_cas, OV5_XIVE_EXPLOIT)) {
> > + } else if (spapr->ov5_cas
> > + && spapr_ovec_test(spapr->ov5_cas, OV5_XIVE_EXPLOIT)) {
> > new_intc = SPAPR_INTC(spapr->xive);
> > } else {
> > new_intc = SPAPR_INTC(spapr->ics);
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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