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

[Kevin Laatz <kevin.laatz@intel.com>]

On 03/09/2022 14:33, Jerin Jacob wrote:
> 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

Thanks for reviewing, Jerin.

I'll look into adding a UT, thanks!