On Mon, 18 Nov 2019 16:37:16 +0100
Cédric Le Goater <c...@kaod.org> wrote:
> On 18/11/2019 16:12, Greg Kurz wrote:
> > When using the XIVE KVM device, the trigger page is directly accessible
> > in QEMU. Unlike with XICS, no need to ask KVM to fire the interrupt. A
> > simple store on the trigger page does the job.
> >
> > Just call xive_esb_trigger().
>
> Yes but the KVM XIVE device does a few other checks.
>
> It checks that the interrupt was correctly initialized at the KVM device
> level. We should be fine in QEMU which has similar checks.
>
Yeah, not sure we can do much more than to trust the QEMU irq code to
pass us a valid srcno.
> It caches the LSI assertion level. We should be fine also because it is
> useless in KVM when using the XIVE native exploitation mode.
>
Yeah, I see it is set in kvmppc_xive_native_set_source() (why?) but never
used anywhere else in book3s_xive_native.c.
> It checks it is not a passthru interrupt. Any idea on how to check this
> condition under QEMU ?
>
AFAICT passthru interrupts don't go through here either.
> > This may improve performance of emulated devices that go through
> > qemu_set_irq(), eg. virtio devices created with ioeventfd=off or
> > configured by the guest to use LSI interrupts, which aren't really
> > recommended setups.
>
> LGTM.
>
> Any figures to share ?
>
No. Since performance critical setups don't go through that path,
I didn't try too much.
> C.
>
> > Signed-off-by: Greg Kurz <gr...@kaod.org>
> > ---
> > hw/intc/spapr_xive_kvm.c | 16 ++--------------
> > 1 file changed, 2 insertions(+), 14 deletions(-)
> >
> > diff --git a/hw/intc/spapr_xive_kvm.c b/hw/intc/spapr_xive_kvm.c
> > index 08012ac7cd76..69e73552f1ef 100644
> > --- a/hw/intc/spapr_xive_kvm.c
> > +++ b/hw/intc/spapr_xive_kvm.c
> > @@ -354,32 +354,20 @@ static void kvmppc_xive_source_get_state(XiveSource
> > *xsrc)
> > void kvmppc_xive_source_set_irq(void *opaque, int srcno, int val)
> > {
> > XiveSource *xsrc = opaque;
> > - SpaprXive *xive = SPAPR_XIVE(xsrc->xive);
> > - struct kvm_irq_level args;
> > - int rc;
> > -
> > - /* The KVM XIVE device should be in use */
> > - assert(xive->fd != -1);
> >
> > - args.irq = srcno;
> > if (!xive_source_irq_is_lsi(xsrc, srcno)) {
> > if (!val) {
> > return;
> > }
> > - args.level = KVM_INTERRUPT_SET;
> > } else {
> > if (val) {
> > xsrc->status[srcno] |= XIVE_STATUS_ASSERTED;
> > - args.level = KVM_INTERRUPT_SET_LEVEL;
> > } else {
> > xsrc->status[srcno] &= ~XIVE_STATUS_ASSERTED;
> > - args.level = KVM_INTERRUPT_UNSET;
> > }
> > }
> > - rc = kvm_vm_ioctl(kvm_state, KVM_IRQ_LINE, &args);
> > - if (rc < 0) {
> > - error_report("XIVE: kvm_irq_line() failed : %s", strerror(errno));
> > - }
> > +
> > + xive_esb_trigger(xsrc, srcno);
> > }
>
>
