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diff --git a/docs/userguide/tuning.userguide.rst b/docs/userguide/tuning.userguide.rst deleted file mode 100644 index 3673ae2d4..000000000 --- a/docs/userguide/tuning.userguide.rst +++ /dev/null @@ -1,102 +0,0 @@ -.. This work is licensed under a Creative Commons Attribution 4.0 International License. - -.. http://creativecommons.org/licenses/by/4.0 - -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. |