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

[Punit Agrawal <punitagrawal@gmail.com>]

Hi Joseph,

Joseph Salisbury <josephtsalisbury@gmail.com> writes:

> On Thu, Oct 14, 2021 at 3:13 AM Punit Agrawal <punitagrawal@gmail.com> wrote:
>>
>> 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
>>
>
> Hi Punit,
>
> Thanks for your contributions!
>
> I noticed there were no commit messages for patches 1 and 5.

If you look closely, patch 1 does have a commit log.

I missed adding a commit log for patch 5 - but the gist of it is to drop
function declarations when they are not required. In this case, this is
achieved by having the caller defined after all the callees have been
defined.

I'll add a log if the patch gets reposted.

Thanks for taking a look.

Punit

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