== Latency tuning guidelines ==

Many of our tutorials and applications depend on reliabile, low latency processing. 

This is a rough checklist of steps for creating an image (e.g. baseline_1804_lowlatency) that has minimized deterministic latency.

factors affecting this:
* maximum stable processor clock speed
  * we cannot depend on boost states (intel turbo boost), as they can't be maintained under all load conditions, or for many cores.
  * it is possible to fix a small number of cores to a high boost by disabling others, but this usually requires bios support
* number of cpus
  * systems with multiple cpus can introduce latency with communication between them. Single cpu systems are much simpler to optimize
  * NUMA issues: with multiple cpus, you must pay close attention to which memory is allocated to which cpu, as well as where pcie devices are attached.


1. Choosing node to use:
  * from above, pick a node with a single cpu, and the maximum clock available
1. install a low latency kernel
 * {{{ apt install linux-lowlatency-hwe-18.04 linux-tools-lowlatency-hwe-18.04}}}
1. usage of tuned-adm
  * tuned is a perfomance optimization project that wraps many configuration methods
  * {{{ apt install tuned }}}


== Monitoring tools ==

* htop
* i7z
* hwloc (to show pci and numa layout)


== Results
r740 results
|| transition latency || cstate ||
|| 1 || 0 ||
|| 2 || 1 ||
|| 10 || 10 ||


|| tuned latency || cstate || workload || mhz ||
|| 1 || 0 || idle || 3300 ||
|| 1 || 0 || stress -c 48 || 3300 ||
|| 1 || 0 || stress --matrix 48 || 3000 ||
|| 1 || 0 || mprime -t || 2300 ||



* USRP 2974:
  * C0 2500mhz all core
  * C0 2300mhz stress --matrix 0
  * C0 2000mhz prime95 avx
* dell r740xd xeon gold
  * 3300mhz c0 all core
  * 3000mhz c0 stress-ng --matrix 0
  * 2300mhz c0 p95 avx512