Re: [dpdk-dev] [PATCH 0/5] add apistats function

[David Hunt <david.hunt@intel.com>]

On 4/12/2020 7:51 AM, Hideyuki Yamashita wrote:
> In general, DPDK application consumes CPU usage because it polls
> incoming packets using rx_burst API in infinite loop.
> This makes difficult to estimate how much CPU usage is really
> used to send/receive packets by the DPDK application.
>
> For example, even if no incoming packets arriving, CPU usage
> looks nearly 100% when observed by top command.
>
> It is beneficial if developers can observe real CPU usage of the
> DPDK application.
> Such information can be exported to monitoring application like
> prometheus/graphana and shows CPU usage graphically.
>
> To achieve above, this patch set provides apistats functionality.
> apistats provides the followiing two counters for each lcore.
> - rx_burst_counts[RTE_MAX_LCORE]
> - tx_burst_counts[RTE_MAX_LCORE]
> Those accumulates rx_burst/tx_burst counts since the application starts.
>
> By using those values, developers can roughly estimate CPU usage.
> Let us assume a DPDK application is simply forwarding packets.
> It calls tx_burst only if it receive packets.
> If rx_burst_counts=1000 and tx_burst_count=1000 during certain
> period of time, one can assume CPU usage is 100%.
> If rx_burst_counts=1000 and tx_burst_count=100 during certain
> period of time, one can assume CPU usage is 10%.
> Here we assumes that tx_burst_count equals counts which rx_burst function
> really receives incoming packets.
>
>
> This patch set provides the following.
> - basic API counting functionality(apistats) into librte_ethdev
> - add code to testpmd to accumulate counter information
> - add code to proc-info to retrieve above mentioned counter information
> - add description in proc-info document about --apistats parameter
> - modify MAINTAINERS file for apistats.c and apistats.h
>
> Hideyuki Yamashita (5):
>    maintainers: update maintainers file for apistats
>    app/proc-info: add to use apistats
>    app/test-pmd: add to use apistats
>    docs: add description of apistats parameter into proc-info
>    librte_ethdev: add to use apistats
>
>   MAINTAINERS                      |  3 ++
>   app/proc-info/main.c             | 46 +++++++++++++++++++++++
>   app/test-pmd/testpmd.c           |  4 ++
>   doc/guides/tools/proc_info.rst   | 10 ++++-
>   lib/librte_ethdev/meson.build    |  6 ++-
>   lib/librte_ethdev/rte_apistats.c | 64 ++++++++++++++++++++++++++++++++
>   lib/librte_ethdev/rte_apistats.h | 64 ++++++++++++++++++++++++++++++++
>   lib/librte_ethdev/rte_ethdev.h   |  7 ++++
>   lib/librte_ethdev/version.map    |  5 +++
>   9 files changed, 205 insertions(+), 4 deletions(-)
>   create mode 100644 lib/librte_ethdev/rte_apistats.c
>   create mode 100644 lib/librte_ethdev/rte_apistats.h


Hi Hideyuki,

I have a few questions on the patch set.

How does this compare to the mechanism added to l3fwd-power which counts 
the number of empty, partial and full polls, and uses them to calculate 
busyness? We saw pretty good tracking of busyness using those metrics. I 
would be concerned that just looking at the numebr of rx_bursts and 
tx_bursts may be limited to only a few use-cases. The l3fwd-power 
example uses branchless increments to capture empty, non-empty, full, 
and non-full polls.

Why not use the existing telemetry library to store the stats? It would 
be good if whatever metrics were counted were made available in a 
standard way, so that external entities such as collectd could pick them 
up, rather than having to parse the new struct. The l3fwd-power example 
registers the necessary new metrics, and exposes them through the 
telemetry library.

And a comment on the patch set in general: The order of the patch set 
seems reversed. The earlier patch do not compile, because they depend on 
rte_apistats.h, which is introduced in the final patch. Each patch as it 
is applied needs to build successfully.

Also, I would suggest a different name. rte_apistats seems very generic 
and could apply to anything. How about something like rte_ethdev_stats.h 
or rte_burst_stats.h?

Rgds,
Dave.