If transmitting uncompressed video stream to achieve optimal performance with high definition video, it may be necessary to tune your system's network parameters to more aggressive values than used by default.
A key factor affecting performance is the path MTU. It is unlikely that the system will sustain gigabit rates with the 1500 octet Ethernet MTU. If using a gigabit Ethernet you may be able to improve performance by setting an 8192 octet MTU on the interface, provided all intermediate hops on the path from sender to receiver support the large MTU.
UltraGrid attempts to increase the UDP receive socket buffer from the default value (typically 64 kilobytes) to 4/6 megabytes. If successful, this will make the system more robust to scheduling variations and better able to accept bursty packet arrivals. UltraGrid will notify you if it cannot increase buffers. You should follow those instructions and set your system according to it.
Interrupt processing load on the receiver host may be significant when running at high rates. Depending on your network interface hardware it may be possible to coalesce interrupts to reduce this load, although the settings to do this are highly driver dependent. On FreeBSD, the use of network device polling may also help performance: see the man page for "polling" in section 4 of the manual.
In many cases, the performance of your network interface card may be limited by host bus performance (this is particularly an issue at high rates, for example when using HD format video).
If using a HW grabbing card (eg. DVS) as a display device, the key factor limiting performance is PCI bus contention. Ensure that the grabbing card is on a separate PCI bus to the network card -- this typically requires a server class motherboard. On Linux, the PCI bus topology can be displayed using "lspci -tv", for example:
[root@ormal root]# lspci -tv
-+-[03]---06.0 Xilinx, Inc.: Unknown device d150
+-[01]-+-02.0-[02]--+-04.0 Adaptec 7899P
| | \-04.1 Adaptec 7899P
| \-0e.0 3Com Corporation 3c985 1000BaseSX
\-[00]-+-00.0 ServerWorks CNB20HE
+-00.1 ServerWorks CNB20HE
+-00.2 ServerWorks: Unknown device 0006
+-00.3 ServerWorks: Unknown device 0006
+-04.0 Intel Corporation 82557 [Ethernet Pro 100]
+-0e.0 ATI Technologies Inc Rage XL
+-0f.0 ServerWorks OSB4
\-0f.1 ServerWorks: Unknown device 0211
[root@ormal root]#
showing an DVS card on PCI bus [03] (the card shows as a Xilinx device) and a gigabit Ethernet card on PCI bus [02] (the 3Com entry).
For software display, you can use SDL or OpenGL display. Both are accelerated (Mac and Linux) if you have properly configured video drivers. On Linux, basic operability can be checked with following commands. If configured properly, both should display driver properties: [root@ormal root]# glxinfo <-- output omitted --> and for SDL (accelerated through XVideo: [root@ormal root]# xvinfo <-- output omitted -->
If you intend to use some of DXT compressions, recommended driver is OpenGL, which can display it natively. When using other display drivers, decompression is still done throught OpenGL and then displayed with requested video driver.
Note: This is left only as a legacy behavior - currently UltraGrid is intended to run without real-time priority (although still being able to compiled with it). This may not be recommended in a general case, however.
The UltraGrid system will attempt to enable POSIX real-time scheduling to improve performance. This behaviour is disabled by default now, because it can occupy the whole system when enabled, but it can be stil enabled by '--enable-rt' configure option. If you see the message:
WARNING: Unable to set real-time scheduling
when starting the application, this means that the operating system did not permit it to enable real-time scheduling. The application will run, but with reduced performance. The most likely reason for failure to set realtime scheduling is that the application has insufficient privilege: it should either be run by root, or be made setuid root. A similar message:
WARNING: System does not support real-time scheduling
indicates that your operating system does not support POSIX real-time scheduling. The application will still run, but performance may be less than desired.
You can find more operating system tweaks at this page: https://github.com/CESNET/UltraGrid/wiki/OS-Setup-UltraGrid