+++ /dev/null
-.. This work is licensed under a Creative Commons Attribution 4.0 International License.
-.. http://creativecommons.org/licenses/by/4.0
-.. (c) <optionally add copywriters name>
-
-Low Latency Tunning Suggestion
-==============================
-
-The correct configuration is critical for improving the NFV performance/latency.
-Even working on the same codebase, configurations can cause wildly different
-performance/latency results.
-
-There are many combinations of configurations, from hardware configuration to
-Operating System configuration and application level configuration. And there
-is no one simple configuration that works for every case. To tune a specific
-scenario, it's important to know the behaviors of different configurations and
-their impact.
-
-Platform Configuration
-----------------------
-
-Some hardware features can be configured through firmware interface(like BIOS)
-but others may not be configurable (e.g. SMI on most platforms).
-
-* **Power management:**
- Most power management related features save power at the
- expensive of latency. These features include: Intel®Turbo Boost Technology,
- Enhanced Intel®SpeedStep, Processor C state and P state. Normally they should
- be disabled but, depending on the real-time application design and latency
- requirements, there might be some features that can be enabled if the impact on
- deterministic execution of the workload is small.
-
-* **Hyper-Threading:**
- The logic cores that share resource with other logic cores can introduce
- latency so the recommendation is to disable this feature for realtime use
- cases.
-
-* **Legacy USB Support/Port 60/64 Emulation:**
- These features involve some emulation in firmware and can introduce random
- latency. It is recommended that they are disabled.
-
-* **SMI (System Management Interrupt):**
- SMI runs outside of the kernel code and can potentially cause
- latency. It is a pity there is no simple way to disable it. Some vendors may
- provide related switches in BIOS but most machines do not have this capability.
-
-Operating System Configuration
-------------------------------
-
-* **CPU isolation:**
- To achieve deterministic latency, dedicated CPUs should be allocated for
- realtime application. This can be achieved by isolating cpus from kernel
- scheduler. Please refer to
- http://lxr.free-electrons.com/source/Documentation/kernel-parameters.txt#L1608
- for more information.
-
-* **Memory allocation:**
- Memory shoud be reserved for realtime applications and usually hugepage should
- be used to reduce page fauts/TLB misses.
-
-* **IRQ affinity:**
- All the non-realtime IRQs should be affinitized to non realtime CPUs to
- reduce the impact on realtime CPUs. Some OS distributions contain an irqbalance
- daemon which balances the IRQs among all the cores dynamically. It should be
- disabled as well.
-
-* **Device assignment for VM:**
- If a device is used in a VM, then device passthrough is desirable. In this case,
- the IOMMU should be enabled.
-
-* **Tickless:**
- Frequent clock ticks cause latency. CONFIG_NOHZ_FULL should be enabled in the
- linux kernel. With CONFIG_NOHZ_FULL, the physical CPU will trigger many fewer
- clock tick interrupts(currently, 1 tick per second). This can reduce latency
- because each host timer interrupt triggers a VM exit from guest to host which
- causes performance/latency impacts.
-
-* **TSC:**
- Mark TSC clock source as reliable. A TSC clock source that seems to be
- unreliable causes the kernel to continuously enable the clock source watchdog
- to check if TSC frequency is still correct. On recent Intel platforms with
- Constant TSC/Invariant TSC/Synchronized TSC, the TSC is reliable so the
- watchdog is useless but cause latency.
-
-* **Idle:**
- The poll option forces a polling idle loop that can slightly improve the
- performance of waking up an idle CPU.
-
-* **RCU_NOCB:**
- RCU is a kernel synchronization mechanism. Refer to
- http://lxr.free-electrons.com/source/Documentation/RCU/whatisRCU.txt for more
- information. With RCU_NOCB, the impact from RCU to the VNF will be reduced.
-
-* **Disable the RT throttling:**
- RT Throttling is a Linux kernel mechanism that
- occurs when a process or thread uses 100% of the core, leaving no resources for
- the Linux scheduler to execute the kernel/housekeeping tasks. RT Throttling
- increases the latency so should be disabled.
-
-* **NUMA configuration:**
- To achieve the best latency. CPU/Memory and device allocated for realtime
- application/VM should be in the same NUMA node.
Code Review / kvmfornfv.git / blobdiff