Re: [PATCH v5 1/3] eal: add lcore poll busyness telemetry

[Jerin Jacob <jerinjacobk@gmail.com>]

On Fri, Sep 2, 2022 at 9:26 PM Kevin Laatz <kevin.laatz@intel.com> wrote:
>
> From: Anatoly Burakov <anatoly.burakov@intel.com>
>
> Currently, there is no way to measure lcore poll busyness in a passive way,
> without any modifications to the application. This patch adds a new EAL API
> that will be able to passively track core polling busyness.
>
> The poll busyness is calculated by relying on the fact that most DPDK API's
> will poll for work (packets, completions, eventdev events, etc). Empty
> polls can be counted as "idle", while non-empty polls can be counted as
> busy. To measure lcore poll busyness, we simply call the telemetry
> timestamping function with the number of polls a particular code section
> has processed, and count the number of cycles we've spent processing empty
> bursts. The more empty bursts we encounter, the less cycles we spend in
> "busy" state, and the less core poll busyness will be reported.
>
> In order for all of the above to work without modifications to the
> application, the library code needs to be instrumented with calls to the
> lcore telemetry busyness timestamping function. The following parts of DPDK
> are instrumented with lcore poll busyness timestamping calls:
>
> - All major driver API's:
>   - ethdev
>   - cryptodev
>   - compressdev
>   - regexdev
>   - bbdev
>   - rawdev
>   - eventdev
>   - dmadev
> - Some additional libraries:
>   - ring
>   - distributor
>
> To avoid performance impact from having lcore telemetry support, a global
> variable is exported by EAL, and a call to timestamping function is wrapped
> into a macro, so that whenever telemetry is disabled, it only takes one
> additional branch and no function calls are performed. It is disabled at
> compile time by default.
>
> This patch also adds a telemetry endpoint to report lcore poll busyness, as
> well as telemetry endpoints to enable/disable lcore telemetry. A
> documentation entry has been added to the howto guides to explain the usage
> of the new telemetry endpoints and API.
>
> Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
> Signed-off-by: Conor Walsh <conor.walsh@intel.com>
> Signed-off-by: David Hunt <david.hunt@intel.com>
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>

This version looks good to me. Thanks for this new feature.

I think, we need to add a UT for this new rte_lcore_poll_* APIs also
add a performance test case to measure the cycles for
RTE_LCORE_POLL_BUSYNESS_TIMESTAMP [1]

[1]
Reference performance test application for trace: app/test/test_trace_perf.c