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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.
+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
* **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.
+ 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
* **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.
+ provide related switches in BIOS but most machines do not have this
+ capability.
Operating System Configuration
------------------------------
for more information.
* **Memory allocation:**
- Memory shoud be reserved for realtime applications and usually hugepage should
- be used to reduce page fauts/TLB misses.
+ 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.
+ 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.
+ 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.
+ 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.
+ 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
* **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.
+ 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
Code Review / kvmfornfv.git / blobdiff