[PATCH v6 2/5] eal: allow applications to report their cpu usage

[David Marchand]

On Thu, Jan 19, 2023 at 4:08 PM Robin Jarry <rjarry at redhat.com> wrote:
>
> 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>
> ---
>
> Notes:
>     v5 -> v6: Added/rephrased some inline comments.
>
>  lib/eal/common/eal_common_lcore.c | 45 ++++++++++++++++++++++++++++---
>  lib/eal/include/rte_lcore.h       | 35 ++++++++++++++++++++++++
>  lib/eal/version.map               |  1 +
>  3 files changed, 78 insertions(+), 3 deletions(-)
>
> diff --git a/lib/eal/common/eal_common_lcore.c b/lib/eal/common/eal_common_lcore.c
> index 16548977dce8..80513cfe3725 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;
> +}
> +
>  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];

This is a debug/non performance sensitive helper.
Please remove this "big enough for now" buffer and use a dynamic allocation.


> +       struct rte_lcore_usage usage;
> +       rte_lcore_usage_cb usage_cb;
>         const char *role;
>         FILE *f = arg;
>         int ret;
> @@ -446,11 +457,25 @@ lcore_dump_cb(unsigned int lcore_id, void *arg)
>                 break;
>         }
>
> +       /* The callback may not set all the fields in the structure, so clear it here. */
> +       memset(&usage, 0, sizeof(usage));
> +       usage_str[0] = '\0';
> +       /*
> +        * Guard against concurrent modification of lcore_usage_cb.
> +        * rte_lcore_register_usage_cb() should only be called once at application init
> +        * but nothing prevents and application to reset the callback to NULL.
> +        */
> +       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 +514,9 @@ 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;

Reverse xmas tree please.

>
> @@ -522,6 +549,18 @@ 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);
> +       /* The callback may not set all the fields in the structure, so clear it here. */
> +       memset(&usage, 0, sizeof(usage));
> +       /*
> +        * Guard against concurrent modification of lcore_usage_cb.
> +        * rte_lcore_register_usage_cb() should only be called once at application init
> +        * but nothing prevents and application to reset the callback to NULL.
> +        */
> +       usage_cb = lcore_usage_cb;
> +       if (usage_cb != NULL && usage_cb(lcore_id, &usage) == 0) {
> +               rte_tel_data_add_dict_u64(info->d, "total_cycles", usage.total_cycles);
> +               rte_tel_data_add_dict_u64(info->d, "busy_cycles", usage.busy_cycles);
> +       }
>
>         return 0;
>  }
> diff --git a/lib/eal/include/rte_lcore.h b/lib/eal/include/rte_lcore.h
> index 6938c3fd7b81..52468e7120dd 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.

Let's be consistent and use lcore.


> + */
> +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. */

This is confusing to have the comments after.
Please put those comments before the associated fields (using /** ).


> +};
> +
> +/**
> + * Callback to allow applications to report CPU usage.

lcore*

> + *
> + * @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 must not be modified.
> + *   - 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.

lcore*

> + *
> + * @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;

Please start a new block for 23.03 symbols.


-- 
David Marchand