[PATCH 2/4] eal: allow applications to report their cpu usage

[Robin Jarry]

Robin Jarry, Dec 07, 2022 at 17:21:
> Allow applications to register a callback that will be invoked in
> rte_lcore_dump() and when requesting lcore info in the telemetry API.
>
> The callback is expected to return the number of TSC cycles that have
> passed since application start and the number of these cycles that were
> spent doing busy work.
>
> Signed-off-by: Robin Jarry <rjarry at redhat.com>
> Acked-by: Morten Brørup <mb at smartsharesystems.com>
> ---
> v3 -> v4: Changed nomenclature: CPU cycles -> TSC cycles

As you may have noticed, I forgot to add -v4 for that iteration...

> diff --git a/lib/eal/include/rte_lcore.h b/lib/eal/include/rte_lcore.h
> index 6938c3fd7b81..df7f0a8e07c6 100644
> --- a/lib/eal/include/rte_lcore.h
> +++ b/lib/eal/include/rte_lcore.h
> @@ -328,6 +328,35 @@ typedef int (*rte_lcore_iterate_cb)(unsigned int lcore_id, void *arg);
>  int
>  rte_lcore_iterate(rte_lcore_iterate_cb cb, void *arg);
>  
> +/**
> + * Callback to allow applications to report CPU usage.
> + *
> + * @param [in] lcore_id
> + *   The lcore to consider.
> + * @param [out] busy_cycles
> + *   The amount of busy time since application start, in TSC cycles.
> + * @param [out] total_cycles
> + *   The total amount of time since application start, in TSC cycles.
> + * @return
> + *   - 0 if both busy and total were set correctly.
> + *   - a negative value if the information is not available or if any error occurred.
> + */
> +typedef int (*rte_lcore_usage_cb)(
> +	unsigned int lcore_id, uint64_t *busy_cycles, uint64_t *total_cycles);

Instead of two uint64_t pointers, I was thinking a better approach would
be to pass a pointer to a struct containing these two fields. That way
it leaves room for adding more counters if need be. And do so without
breaking the ABI.

Thoughts?