Re: [RFC PATCH] ethdev: add new API for enable/disable xstat counters by ID

[Stephen Hemminger <stephen@networkplumber.org>]

On Sun, 22 Dec 2024 17:38:19 +0200
Shani Peretz <shperetz@nvidia.com> wrote:

> This change introduces a new API to dynamically enable or disable
> xstat counters by their IDs. Some counters may require hardware
> resources that are potentially limited, so providing the ability
> to toggle them on or off makes sense.
> In addition, adding an API to query the current state
> (enabled, disabled, or not supported) of an xstat counter is added.
> New APIs:
> 	- rte_eth_xstats_enable_counter(struct rte_eth_dev *dev, uint64_t id);
> 	- rte_eth_xstats_disable_counter(struct rte_eth_dev *dev, uint64_t id);
> 	- rte_eth_xstats_query_state(struct rte_eth_dev *dev, uint64_t id);
> 
> Added the following testpmd subcommands:
>  toggle the counter on and off
>      > port (port_id) enable|disable <counter_name>  
> query the state of counters:
>      > set xstats-show-state on|off  
> 
> Note that by default, generic stats (like those provided by
> eth_basic_stats_get()) will be considered unsupported and
> will not be toggleable.
> Also all xstats will be considered unsupported for dynamic enable/disable,
> and each PMD will be able to override this in its implementation.
> 
> Specifically in mlx5 PMD, expose a new xstat to track packet drops of
> hairpin Rx queue:
>    - Hairpin_out_of_buffer - Port-level counter -
> 		counts drops from all the hairpin queues
>    - Hairpin_out_of_buffer_rxq* - Queue-level counter -
> 		counts drops of a specific queue
> Both the port-level and per-queue counters can be
> enabled, disabled, and queried.
> 
> Signed-off-by: Shani Peretz <shperetz@nvidia.com>

Why what is the value of having a counter disabled?
Is this something that speeds up the PMD?

IMHO DPDK changes should be driven off user need, not the HW capabilities.