View source for USRP Host Performance Tuning Tips and Tricks

==Application Note Number==
'''AN-088'''

==Overview==
This application note provides various tips and tricks for tuning your host computer for best performance when working with USRP devices.

==CPU Governor==
Ensure your CPU governor is set to <code>performance</code>. This can be done with the Linux utility <code>cpufrequtils</code>.

Install <code>cpufrequtils</code> with the command below:

    sudo apt install cpufrequtils

You can then set the CPU governor to <code>performance</code> per core by issuing the command:

    sudo cpufreq-set -c $core_number -g performance

To set the CPU governor to <code>performance</code> for all cores:

    for ((i=0;i<$(nproc --all);i++)); do sudo cpufreq-set -c $i -r -g performance; done

You can then verify that the CPU governor has been set by running the command:

    cpufreq-info

==Thread Priority Scheduling==

When UHD spawns a new thread, it may try to boost the thread's scheduling priority. If setting the new priority fails, the UHD software prints a warning to the console, as shown below. This warning is harmless; it simply means that the thread will retain a normal or default scheduling priority.

<pre>
UHD Warning:
    Unable to set the thread priority. Performance may be negatively affected.
    Please see the general application notes in the manual for instructions.
    EnvironmentError: OSError: error in pthread_setschedparam
</pre>

To address this issue, non-privileged (non-root) users need to be given special permission to change the scheduling priority. This can be enabled by creating a group <code>usrp</code>, adding your user to it, and then appending the line <code>@usrp - rtprio  99</code> to the file <code>/etc/security/limits.conf</code>.

    sudo groupadd usrp
    sudo usermod -aG usrp $USER

Then add the line below to end of the file <code>/etc/security/limits.conf</code>:

    @usrp - rtprio  99

You must log out and log back into the account for the settings to take effect. In most Linux distributions, a list of groups and group members can be found in the <code>/etc/group</code> file.

There is further documentation about this in the User Manual at the link below.

* [http://files.ettus.com/manual/page_general.html#general_threading_prio Threading Notes section of the User Manual]


==Adjust Network Buffers==
This applies to USRP devices connected via Ethernet, such as the N200, N210, N300, N310, N320, N321, X300, X310, E320.

Note that these settings will not persist across a reboot.

    sudo sysctl -w net.core.wmem_max=33554432
    sudo sysctl -w net.core.rmem_max=33554432
    sudo sysctl -w net.core.wmem_default=33554432
    sudo sysctl -w net.core.rmem_default=33554432

==Adjust Ethernet MTU==
This applies to Ethernet connected USRPs (N2xx, N3xx, X3xx, E320).

For 1 Gigabit connections, the MTU should be set to <code>1500</code>.

For 10 Gigabit connections, the MTU should be set to <code>9000</code>.

It is important to set the value and '''not''' leave it is <code>automatic</code>

==Increasing Ring Buffers==
This applies to Ethernet connected USRPs using a 10 Gb interface (X3xx, N3xx, E320).

Increasing the Ring Buffers on the NIC may help prevent flow control errors at higher rates.

    sudo ethtool -G <interface> tx 4096 rx 4096

== DPDK == 
DPDK is supported on N3xx, X3xx and E320 USRPs. DPDK replaces the traditional Linux networking stack with a low overhead user-land based driver. Additional details of using DPDK can be found in the UHD Manual located at the following link: https://files.ettus.com/manual/page_dpdk.html 

==Disable Hyper-threading==
In some applications which require the highest possible CPU performance per core, disabling hyper-threading can provide roughly a 10% increase in core performance, at the cost of having less core threads. Hyper-threading can be disabled within the BIOs and varies by  manufacturer.

== Disable KPTI Protections for Spectre/Meltdown==
In some cases, disabling the KPTI protections for the Linux Kernel can increase performance by 10-15%. It is important to note the ramification making this modification can have. This modification is only recommended for systems that absolutely require the best performance and are not connected to the internet.

* https://en.wikipedia.org/wiki/Meltdown_(security_vulnerability)
* https://en.wikipedia.org/wiki/Spectre_(security_vulnerability)

Disabling KPTI protections can be done by adding the lines below to your <code>/etc/default/grub</code> file at <code>GRUB_CMDLINE_LINUX_DEFAULT=""</code>

    pti=off spectre_v2=off l1tf=off nospec_store_bypass_disable no_stf_barrier

After modifying the <code>grub</code> file, run the following command to update your configuration and reboot:

    sudo update-grub






[[Category:Application Notes]]