[PATCH v5 2/4] eal: allow applications to report their cpu usage

[Konstantin Ananyev]

> 
> 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>
> ---
> v4 -> v5:
> 
> The callback now takes a pointer to a rte_lcore_usage structure.
> I chose not to include any API version tracking mechanism since the
> unsupported/unused fields can simply be left to zero. This is only
> telemetry after all.
> 
>  lib/eal/common/eal_common_lcore.c | 33 ++++++++++++++++++++++++++---
>  lib/eal/include/rte_lcore.h       | 35 +++++++++++++++++++++++++++++++
>  lib/eal/version.map               |  1 +
>  3 files changed, 66 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/eal/common/eal_common_lcore.c b/lib/eal/common/eal_common_lcore.c
> index 16548977dce8..210636d21d6b 100644
> --- a/lib/eal/common/eal_common_lcore.c
> +++ b/lib/eal/common/eal_common_lcore.c
> @@ -2,6 +2,7 @@
>   * Copyright(c) 2010-2014 Intel Corporation
>   */
> 
> +#include <inttypes.h>
>  #include <stdlib.h>
>  #include <string.h>
> 
> @@ -422,11 +423,21 @@ rte_lcore_iterate(rte_lcore_iterate_cb cb, void *arg)
>  	return ret;
>  }
> 
> +static rte_lcore_usage_cb lcore_usage_cb;
> +
> +void
> +rte_lcore_register_usage_cb(rte_lcore_usage_cb cb)
> +{
> +	lcore_usage_cb = cb;
> +}
> +

LGTM in general.
One question: I assume this function is supposed to be called just once at app init stage,
so we probably don't need to worry about possible sync issues, right?
If so, then probably worth to mention it in the function formal comments below. 

>  static int
>  lcore_dump_cb(unsigned int lcore_id, void *arg)
>  {
>  	struct rte_config *cfg = rte_eal_get_configuration();
> -	char cpuset[RTE_CPU_AFFINITY_STR_LEN];
> +	char cpuset[RTE_CPU_AFFINITY_STR_LEN], usage_str[256];
> +	struct rte_lcore_usage usage;
> +	rte_lcore_usage_cb usage_cb;
>  	const char *role;
>  	FILE *f = arg;
>  	int ret;
> @@ -446,11 +457,19 @@ lcore_dump_cb(unsigned int lcore_id, void *arg)
>  		break;
>  	}
> 
> +	memset(&usage, 0, sizeof(usage));
> +	usage_str[0] = '\0';
> +	usage_cb = lcore_usage_cb;
> +	if (usage_cb != NULL && usage_cb(lcore_id, &usage) == 0) {
> +		snprintf(usage_str, sizeof(usage_str), ", busy cycles %"PRIu64"/%"PRIu64,
> +			usage.busy_cycles, usage.total_cycles);
> +	}
>  	ret = eal_thread_dump_affinity(&lcore_config[lcore_id].cpuset, cpuset,
>  		sizeof(cpuset));
> -	fprintf(f, "lcore %u, socket %u, role %s, cpuset %s%s\n", lcore_id,
> +	fprintf(f, "lcore %u, socket %u, role %s, cpuset %s%s%s\n", lcore_id,
>  		rte_lcore_to_socket_id(lcore_id), role, cpuset,
> -		ret == 0 ? "" : "...");
> +		ret == 0 ? "" : "...", usage_str);
> +
>  	return 0;
>  }
> 
> @@ -489,7 +508,9 @@ lcore_telemetry_info_cb(unsigned int lcore_id, void *arg)
>  {
>  	struct lcore_telemetry_info *info = arg;
>  	struct rte_config *cfg = rte_eal_get_configuration();
> +	struct rte_lcore_usage usage;
>  	struct rte_tel_data *cpuset;
> +	rte_lcore_usage_cb usage_cb;
>  	const char *role;
>  	unsigned int cpu;
> 
> @@ -522,6 +543,12 @@ lcore_telemetry_info_cb(unsigned int lcore_id, void *arg)
>  		if (CPU_ISSET(cpu, &lcore_config[lcore_id].cpuset))
>  			rte_tel_data_add_array_int(cpuset, cpu);
>  	rte_tel_data_add_dict_container(info->d, "cpuset", cpuset, 0);
> +	memset(&usage, 0, sizeof(usage));
> +	usage_cb = lcore_usage_cb;
> +	if (usage_cb != NULL && usage_cb(lcore_id, &usage) == 0) {
> +		rte_tel_data_add_dict_u64(info->d, "busy_cycles", usage.busy_cycles);
> +		rte_tel_data_add_dict_u64(info->d, "total_cycles", usage.total_cycles);
> +	}
> 
>  	return 0;
>  }
> diff --git a/lib/eal/include/rte_lcore.h b/lib/eal/include/rte_lcore.h
> index 6938c3fd7b81..a92313577355 100644
> --- a/lib/eal/include/rte_lcore.h
> +++ b/lib/eal/include/rte_lcore.h
> @@ -328,6 +328,41 @@ typedef int (*rte_lcore_iterate_cb)(unsigned int lcore_id, void *arg);
>  int
>  rte_lcore_iterate(rte_lcore_iterate_cb cb, void *arg);
> 
> +/**
> + * CPU usage statistics.
> + */
> +struct rte_lcore_usage {
> +	uint64_t total_cycles;
> +	/**< The total amount of time since application start, in TSC cycles. */
> +	uint64_t busy_cycles;
> +	/**< The amount of busy time since application start, in TSC cycles. */
> +};
> +
> +/**
> + * Callback to allow applications to report CPU usage.
> + *
> + * @param [in] lcore_id
> + *   The lcore to consider.
> + * @param [out] usage
> + *   Counters representing this lcore usage. This can never be NULL.
> + * @return
> + *   - 0 if fields in usage were updated successfully. The fields that the
> + *       application does not support should be left to their default value.
> + *   - a negative value if the information is not available or if any error occurred.
> + */
> +typedef int (*rte_lcore_usage_cb)(unsigned int lcore_id, struct rte_lcore_usage *usage);
> +
> +/**
> + * Register a callback from an application to be called in rte_lcore_dump() and
> + * the /eal/lcore/info telemetry endpoint handler. Applications are expected to
> + * report CPU usage statistics via this callback.
> + *
> + * @param cb
> + *   The callback function.
> + */
> +__rte_experimental
> +void rte_lcore_register_usage_cb(rte_lcore_usage_cb cb);
> +
>  /**
>   * List all lcores.
>   *
> diff --git a/lib/eal/version.map b/lib/eal/version.map
> index 7ad12a7dc985..30fd216a12ea 100644
> --- a/lib/eal/version.map
> +++ b/lib/eal/version.map
> @@ -440,6 +440,7 @@ EXPERIMENTAL {
>  	rte_thread_detach;
>  	rte_thread_equal;
>  	rte_thread_join;
> +	rte_lcore_register_usage_cb;
>  };
> 
>  INTERNAL {
> --
> 2.38.1