+.. 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/
Code Review / kvmfornfv.git / commitdiff
