The testcase is a rather a very basic one. Doing a mmap on a pcie device and triggering a read and write operation on the Virtual Address, which would in-turn trigger transaction requests on the host device.
I understand that Qemu v4.0 may be and old one, but the issue is that test case execution has become rather very slow with Qemu4.0.0 and the only thing i could notice from using tracebacks were related with increase in KVM_MMIO_EXIT when compared with Qemu2.11.0 version. Can it be verified as to why the number of KVM_EXIT_MMIO has increased drastically in qemu4 when compared to Qemu2.11.0 ? -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1912777 Title: KVM_EXIT_MMIO has increased in Qemu4.0.0 when compared to Qemu 2.11.0 Status in QEMU: Incomplete Status in Ubuntu: New Bug description: I was able to generate trace dump in Qemu for kvm_run_exit event in both QEMU 2.11.0 and QEMU 4.0.0 From the trace i noticed that the number of KVM_KXIT_MMIO calls has increased alot and is causing delay in testcase execution. I executed same testcase from Qemu 2.11 and Qemu4. Inside Virtual machine when using qemu 2.11 testcase got completed in 11 seconds but the same testcase when executed on Qemu 4.0.0 got executed in 26 seconds. I did a bit of digging and extracted the kvm_run_exit to figure out whats going on. Please find Stats from Qemu2.11: KVM_EXIT_UNKNOWN : 0 KVM_EXIT_EXCEPTION : 0 KVM_EXIT_IO : 182513 KVM_EXIT_HYPERCALL : 0 KVM_EXIT_DEBUG : 0 KVM_EXIT_HLT : 0 KVM_EXIT_MMIO : 216701 KVM_EXIT_IRQ_WINDOW_OPEN : 0 KVM_EXIT_SHUTDOWN : 0 KVM_EXIT_FAIL_ENTRY : 0 KVM_EXIT_INTR : 0 KVM_EXIT_SET_TPR : 0 KVM_EXIT_TPR_ACCESS : 0 KVM_EXIT_S390_SIEIC : 0 KVM_EXIT_S390_RESET : 0 KVM_EXIT_DCR : 0 KVM_EXIT_NMI : 0 KVM_EXIT_INTERNAL_ERROR : 0 KVM_EXIT_OSI : 0 KVM_EXIT_PAPR_HCALL : 0 KVM_EXIT_S390_UCONTROL : 0 KVM_EXIT_WATCHDOG : 0 KVM_EXIT_S390_TSCH : 0 KVM_EXIT_EPR : 0 KVM_EXIT_SYSTEM_EVENT : 0 KVM_EXIT_S390_STSI : 0 KVM_EXIT_IOAPIC_EOI : 0 KVM_EXIT_HYPERV : 0 KVM_RUN_EXIT : 399214 (Total in Qemu 2.11 for a testcase) Stats For Qemu 4.0.0: VM_EXIT_UNKNOWN : 0 KVM_EXIT_EXCEPTION : 0 KVM_EXIT_IO : 163729 KVM_EXIT_HYPERCALL : 0 KVM_EXIT_DEBUG : 0 KVM_EXIT_HLT : 0 KVM_EXIT_MMIO : 1094231 KVM_EXIT_IRQ_WINDOW_OPEN : 46 KVM_EXIT_SHUTDOWN : 0 KVM_EXIT_FAIL_ENTRY : 0 KVM_EXIT_INTR : 0 KVM_EXIT_SET_TPR : 0 KVM_EXIT_TPR_ACCESS : 0 KVM_EXIT_S390_SIEIC : 0 KVM_EXIT_S390_RESET : 0 KVM_EXIT_DCR : 0 KVM_EXIT_NMI : 0 KVM_EXIT_INTERNAL_ERROR : 0 KVM_EXIT_OSI : 0 KVM_EXIT_PAPR_HCALL : 0 KVM_EXIT_S390_UCONTROL : 0 KVM_EXIT_WATCHDOG : 0 KVM_EXIT_S390_TSCH : 0 KVM_EXIT_EPR : 0 KVM_EXIT_SYSTEM_EVENT : 0 KVM_EXIT_S390_STSI : 0 KVM_EXIT_IOAPIC_EOI : 464 KVM_EXIT_HYPERV : 0 KVM_RUN_EXIT : 1258470 (Total in qemu 4.0.0 for same testcase) From above analysis i found that the number of KVM_EXIT_MMIO has increased by 4.x. Could someone from qemu community help me understand as to why the MMIO exits have increased in qemu4 ? The results i obtained are after running same testcase. On Qemu2.11 testcase gets completed in : 11seconds on Qemu4.11 testcase gets completed in : 26 seconds VM Qcow2 used in Ubuntu 16.04 VM kernel OS is : 4.4 generic Let me know incase more information is required . To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1912777/+subscriptions
