Re: [PATCH v7 0/4] Add lcore poll busyness telemetry

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

On 14/09/2022 15:33, Stephen Hemminger wrote:
> On Wed, 14 Sep 2022 10:29:25 +0100
> Kevin Laatz <kevin.laatz@intel.com> wrote:
>
>> Currently, there is no way to measure lcore polling busyness in a passive
>> way, without any modifications to the application. This patchset adds a new
>> EAL API that will be able to passively track core polling busyness. As part
>> of the set, new telemetry endpoints are added to read the generate metrics.
> How much does measuring busyness impact performance??
>
> In the past, calling rte_rdsc() would slow down packet rate
> because it is stops CPU pipeline. Maybe better on more modern
> processors, haven't measured it lately.

Hi Stephen,

I've run some 0.001% loss tests using 2x 100G ports, with 64B packets 
using testpmd for forwarding. Those tests show a ~2.7% performance 
impact when the lcore poll busyness feature is enabled vs compile-time 
disabled.
Applications with more compute intensive workloads should see less 
performance impact since the proportion of time spent time-stamping will 
be smaller.

In addition, a performance autotest has been added in this patchset 
which measures the cycles cost of calling the timestamp macro. Please 
feel free to test it on your system (lcore_poll_busyness_perf_autotest).

-Kevin