On 10/8/25 8:51 AM, Thomas Huth wrote: > On 07/10/2025 22.56, Matthew Rosato wrote: >> Allow irqfd to be used for virtio-pci on s390x if the kernel supports >> it. This improves s390x virtio-pci performance when using kvm >> acceleration by allowing kvm to deliver interrupts instead of QEMU. >> >> Reviewed-by: Eric Farman <[email protected]> >> Signed-off-by: Matthew Rosato <[email protected]> >> --- >> v2: >> - add review tag >> - tweak commit message (David) >> --- >> hw/s390x/s390-pci-bus.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c >> index e8e41c8a9a..88852acf45 100644 >> --- a/hw/s390x/s390-pci-bus.c >> +++ b/hw/s390x/s390-pci-bus.c >> @@ -900,6 +900,7 @@ static void s390_pcihost_realize(DeviceState *dev, Error >> **errp) >> s390_pci_init_default_group(); >> css_register_io_adapters(CSS_IO_ADAPTER_PCI, true, false, >> S390_ADAPTER_SUPPRESSIBLE, errp); >> + kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled(); >> } > > Hi Matthew, > > this unfortunately fails to compile without KVM (e.g. on x86 hosts): > > ../../devel/qemu/hw/s390x/s390-pci-bus.c: In function ‘s390_pcihost_realize’: > ../../devel/qemu/hw/s390x/s390-pci-bus.c:903:5: error: > ‘kvm_msi_via_irqfd_allowed’ undeclared (first use in this function); did you > mean ‘kvm_msi_via_irqfd_enabled’? > 903 | kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled(); > | ^~~~~~~~~~~~~~~~~~~~~~~~~ > | kvm_msi_via_irqfd_enabled > ../../devel/qemu/hw/s390x/s390-pci-bus.c:903:5: note: each undeclared > identifier is reported only once for each function it appears in >
Argh, thanks for pointing this out. Of course this value only exists when CONFIG_KVM... What do you think about using a routine in hw/s390x/s390-pci-kvm.c to set the value (and is a NOP stub when !CONFIG_KVM)? Thanks, Matt
