[RFC 0/7] rt-tests: cyclictest: Add support to report standard deviation

[Punit Agrawal <punitagrawal@gmail.com>]

Hi,

Standard deviation is an important measure to evaluate the latency
response of a real time system. It is calculated by downstream tools
such as rteval but the value cannot be correctly calculated when the
latency value exceeds the range of histogram.

This series adds support to report the streaming standard deviation of
latencies to cyclictest. This approach avoids having to track all
latency values and adds minimal overhead (two additional doubles and
compute steps) to each iteration.

In terms of patch organization, the first 5 patches are clean-ups that
were noticed in the course of developing the support for standard
deviation. It should be possible to apply them indepndently.

Patch 6 converts the existing average calculation to a streaming
version. This running average value is needed for the standard
deviation.

Patch 7 finally adds support for calculating standard deviation.

The changes were verified by capturing the latency samples and
verifying the average and standard deviation with manual calculation.

All feedback welcome.

Thanks,
Punit

Punit Agrawal (7):
  rt-tests: cyclictest: Drop unused defines
  rt-tests: cyclictest: Simplify duplicate initialization of "stop"
  rt-tests: cyclictest: Drop unnecessary variable "stopped"
  rt-tests: cyclictest: Drop unnecessary variable "bufsize"
  rt-tests: cyclictest: Move signal handler to avoid function
    declaration
  rt-tests: cyclictest: Use streaming algorithm to calculate averages
  rt-tests: cyclictest: Add support to report standard deviation

 Makefile                    |   2 +-
 src/cyclictest/cyclictest.c | 149 +++++++++++++++++++++---------------
 2 files changed, 87 insertions(+), 64 deletions(-)

-- 
2.32.0