Hi,
I noticed a perf issue in my own pci device, and managed to reproduce it with the pci-testdev with a small patch. Here: 1. diff --git a/hw/misc/pci-testdev.c b/hw/misc/pci-testdev.c 2. index 188de4d9cc..b2e225d25b 100644 3. --- a/hw/misc/pci-testdev.c 4. +++ b/hw/misc/pci-testdev.c 5. @@ -252,7 +252,7 @@ static void pci_testdev_realize(PCIDevice *pci_dev , Error **errp) 6. pci_conf[PCI_INTERRUPT_PIN] = 0; /* no interrupt pin */ 7. 8. memory_region_init_io(&d->mmio, OBJECT(d), &pci_testdev_mmio_ops, d, 9. - "pci-testdev-mmio", IOTEST_MEMSIZE * 2); 10. + "pci-testdev-mmio", 256 * 1024 * 1024); 11. memory_region_init_io(&d->portio, OBJECT(d), &pci_testdev_pio_ops, d, 12. "pci-testdev-portio", IOTEST_IOSIZE * 2); 13. pci_register_bar(pci_dev, 0, PCI_BASE_ADDRESS_SPACE_MEMORY, &d->mmio ); Before my patch, I could start a VM with 32 of these devices happily. I can ssh to the VM within a minute. I also see that once the VM is up, I see small amount of kvm activity, i.e. less than 100 kvm exits a second. After the patch, I can start no more than 3 devices. If I do, I seems like QEMU gets to a state of thrashing. The VM never comes up, and I see the following: kvm statistics - summary Event Total %Total CurAvg/s kvm_fpu 52166411 46.8 2773738 kvm_userspace_exit 26083186 23.4 1386869 kvm_vcpu_wakeup 25415616 22.8 1386869 I tried to trace the kvm exit reason, but I get: qemu-system-x86 83801 [090] 10892345.982869: kvm:kvm_userspace_exit: reason KVM_EXIT_UNKNOWN (0) I am wondering if this is known performance limitation on io memory region? Is there a way around it? Thanks, Mo
