diff options
Diffstat (limited to 'docs/design/kvmfornfv_design.rst')
| -rw-r--r-- | docs/design/kvmfornfv_design.rst | 155 |
1 files changed, 155 insertions, 0 deletions
diff --git a/docs/design/kvmfornfv_design.rst b/docs/design/kvmfornfv_design.rst new file mode 100644 index 000000000..54dcd120a --- /dev/null +++ b/docs/design/kvmfornfv_design.rst @@ -0,0 +1,155 @@ +.. This work is licensed under a Creative Commons Attribution 4.0 International License. +.. http://creativecommons.org/licenses/by/4.0 + +============ +Introduction +============ + +**Purpose**: + + This document provides an overview of the areas that can be addressed to + enhance the KVM Hypervisor for NFV. It is intended to capture and convey the + significant changes which have been made on the KVM Hypervisor. + + +=================== +Project description +=================== + +The NFV hypervisors provide crucial functionality in the NFV +Infrastructure(NFVI).The existing hypervisors, however, are not necessarily +designed or targeted to meet the requirements for the NFVI. + +This design focuses on the enhancement of following area for KVM Hypervisor + +* Minimal Interrupt latency variation for data plane VNFs: + * Minimal Timing Variation for Timing correctness of real-time VNFs + * Minimal packet latency variation for data-plane VNFs +* Fast live migration + +While these items require software development and/or specific hardware features +there are also some adjustments that need to be made to system configuration +information, like hardware, BIOS, OS, etc. + +**Minimal Interrupt latency variation for data plane VNFs** + +Processing performance and latency depend on a number of factors, including +the CPUs (frequency, power management features, etc.), micro-architectural +resources, the cache hierarchy and sizes, memory (and hierarchy, such as NUMA) +and speed, inter-connects, I/O and I/O NUMA, devices, etc. + +There are two separate types of latencies to minimize: + + 1. Minimal Timing Variation for Timing correctness of real-time + VNFs – timing correctness for scheduling operations(such as Radio scheduling) + 2. Minimal packet latency variation for data-plane VNFs – packet delay + variation, which applies to packet processing. + +For a VM, interrupt latency (time between arrival of H/W interrupt and +invocation of the interrupt handler in the VM), for example, can be either of +the above or both, depending on the type of the device. Interrupt latency with +a (virtual) timer can cause timing correctness issues with real-time VNFs even +if they only use polling for packet processing. + +We assume that the VNFs are implemented properly to minimize interrupt latency +variation within the VMs, but we have additional causes of latency variation +on KVM: + + - Asynchronous (e.g. external interrupts) and synchronous(e.g. instructions) + VM exits and handling in KVM (and kernel routines called), which may have + loops and spin locks + - Interrupt handling in the host Linux and KVM, scheduling and virtual + interrupt delivery to VNFs + - Potential VM exit (e.g. EOI) in the interrupt service routines in VNFs + - Exit to the user-level (e.g. QEMU) + +.. Figure:: kvm1.png + +===================== +Design Considerations +===================== + +The latency variation and jitters can be minimized with the below +steps (with some in parallel): + + 1. Statically and exclusively assign hardware resources + (CPUs, memory, caches,) to the VNFs. + + 2. Pre-allocate huge pages (e.g. 1 GB/2MB pages) and guest-to-host mapping, + e.g. EPT (Extended Page Table) page tables, to minimize or mitigate + latency from misses in caches, + + 3. Use the host Linux configured for hard real-time and packet latency, + Check the set of virtual devices used by the VMs to optimize or + eliminate virtualization overhead if applicable + + 4. Use advanced hardware virtualization features that can reduce or + eliminate VM exits, if present, and + + 5. Inspect the code paths in KVM and associated kernel services to + eliminate code that can cause latencies (e.g. loops and spin locks). + + 6. Measure latencies intensively. We leverage the existing testing methods. + OSADL, for example, defines industry tests for timing correctness. + +==================== +Goals and Guidelines +==================== + +The output of this project will provide : + + 1. A list of the performance goals, which will be obtained by the + OPNFV members (as described above) + + 2. A set of comprehensive instructions for the system configurations + (hardware features, BIOS setup, kernel parameters, VM configuration, + options to QEMU/KVM, etc.) + + 3. The above features to the upstream of Linux, the real-time patch + set, KVM, QEMU, libvirt, and + + 4. Performance and interrupt latency measurement tools + +========= +Test plan +========= + +The tests that need to be conducted to make sure that all components from OPNFV +meet the requirement are mentioned below: + +**Timer test**:This test utilize the cyclictest +(https://rt.wiki.kernel.org/index.php/Cyclictest) to test the guest timer +latency (the latency from the time that the guest timer should be triggered +to the time the guest timer is really triggered). + +.. Figure:: TimerTest.png + +**Device Interrupt Test**:A device on the hardware platform trigger interrupt +every one ms and the device interrupt will be delivered to the VNF. This test +cover the latency from the interrupt happened on the hardware to the time the +interrupt handled in the VNF. + +.. Figure:: DeviceInterruptTest.png + +**Packet forwarding (DPDK OVS)**:A packet is sent from TC (Traffic Generator) +to a VNF. The VNF, after processing the packet, forwards the packet to another +NIC and in the end the packet is received by the traffic generator. The test +check the latency from the packet is sent out by the TC to the time the packet +is received by the TC. + +.. Figure:: PacketforwardingDPDK_OVS.png + +**Packet Forwarding (SR-IOV)**:This test is similar to Packet Forwarding +(DPDK OVS). However, instead of using virtio NIC devices on the guest, +a PCI NIC or a PCI VF NIC is assigned to the guest for network acess. + +**Bare-metal Packet Forwarding**:This is used to compare with the above +packet forwarding scenario. + +.. Figure:: Bare-metalPacketForwarding.png + +========= +Reference +========= + +https://wiki.opnfv.org/display/kvm/ |