Re: [dpdk-dev] [PATCH 7/7] eal: add lcore hotplug notifications

["Kinsella, Ray" <mdr@ashroe.eu>]

From ABI  PoV, you are 100%.

Is the agreed term 'callback'?, not 'notifier' for example rte_dev_event_callback_register, rte_mem_event_callback_register

I did wonder however, if all these cb's would be better handled through a EventDev event notification style approach.

Ray K

On 10/06/2020 15:45, David Marchand wrote:
> Now that lcores can be dynamically allocated/freed, we will have to
> notify DPDK components and applications of such events for cases where
> per lcore context must be allocated/initialised.
>
> Signed-off-by: David Marchand <david.marchand@redhat.com>
> ---
>  lib/librte_eal/common/eal_common_lcore.c  | 91 +++++++++++++++++++++++
>  lib/librte_eal/common/eal_common_thread.c | 11 ++-
>  lib/librte_eal/common/eal_private.h       | 26 +++++++
>  lib/librte_eal/include/rte_lcore.h        | 49 ++++++++++++
>  lib/librte_eal/rte_eal_version.map        |  2 +
>  5 files changed, 178 insertions(+), 1 deletion(-)
>
> diff --git a/lib/librte_eal/common/eal_common_lcore.c b/lib/librte_eal/common/eal_common_lcore.c
> index 6aca1b2fee..3a997d8115 100644
> --- a/lib/librte_eal/common/eal_common_lcore.c
> +++ b/lib/librte_eal/common/eal_common_lcore.c
> @@ -212,6 +212,47 @@ rte_socket_id_by_idx(unsigned int idx)
>  	return config->numa_nodes[idx];
>  }
>  
> +struct lcore_notifier {
> +	TAILQ_ENTRY(lcore_notifier) next;
> +	rte_lcore_notifier_cb cb;
> +	void *arg;
> +};
> +static TAILQ_HEAD(lcore_notifiers_head, lcore_notifier) lcore_notifiers =
> +	TAILQ_HEAD_INITIALIZER(lcore_notifiers);
> +static rte_spinlock_t lcore_notifiers_lock = RTE_SPINLOCK_INITIALIZER;
> +
> +void *
> +rte_lcore_notifier_register(rte_lcore_notifier_cb cb, void *arg)
> +{
> +	struct lcore_notifier *notifier;
> +
> +	if (cb == NULL)
> +		return NULL;
> +
> +	notifier = calloc(1, sizeof(*notifier));
> +	if (notifier == NULL)
> +		return NULL;
> +
> +	notifier->cb = cb;
> +	notifier->arg = arg;
> +	rte_spinlock_lock(&lcore_notifiers_lock);
> +	TAILQ_INSERT_TAIL(&lcore_notifiers, notifier, next);
> +	rte_spinlock_unlock(&lcore_notifiers_lock);
> +
> +	return notifier;
> +}
> +
> +void
> +rte_lcore_notifier_unregister(void *handle)
> +{
> +	struct lcore_notifier *notifier = handle;
> +
> +	rte_spinlock_lock(&lcore_notifiers_lock);
> +	TAILQ_REMOVE(&lcore_notifiers, notifier, next);
> +	rte_spinlock_unlock(&lcore_notifiers_lock);
> +	free(notifier);
> +}
> +
>  rte_spinlock_t external_lcore_lock = RTE_SPINLOCK_INITIALIZER;
>  
>  unsigned int
> @@ -277,3 +318,53 @@ rte_lcore_dump(FILE *f)
>  	}
>  	rte_spinlock_unlock(&external_lcore_lock);
>  }
> +
> +int
> +eal_lcore_external_notify_allocated(unsigned int lcore_id)
> +{
> +	struct lcore_notifier *notifier;
> +	int ret = 0;
> +
> +	RTE_LOG(DEBUG, EAL, "New lcore %u.\n", lcore_id);
> +	rte_spinlock_lock(&lcore_notifiers_lock);
> +	TAILQ_FOREACH(notifier, &lcore_notifiers, next) {
> +		if (notifier->cb(lcore_id, RTE_LCORE_EVENT_NEW_EXTERNAL,
> +				notifier->arg) == 0)
> +			continue;
> +
> +		/* Some notifier refused the new lcore, inform all notifiers
> +		 * that acked it.
> +		 */
> +		RTE_LOG(DEBUG, EAL, "A lcore notifier refused new lcore %u.\n",
> +			lcore_id);
> +
> +		notifier = TAILQ_PREV(notifier, lcore_notifiers_head, next);
> +		while (notifier != NULL) {
> +			notifier->cb(lcore_id,
> +				RTE_LCORE_EVENT_RELEASE_EXTERNAL,
> +				notifier->arg);
> +			notifier = TAILQ_PREV(notifier, lcore_notifiers_head,
> +				next);
> +		}
> +		ret = -1;
> +		break;
> +	}
> +	rte_spinlock_unlock(&lcore_notifiers_lock);
> +
> +	return ret;
> +}
> +
> +void
> +eal_lcore_external_notify_removed(unsigned int lcore_id)
> +{
> +	struct lcore_notifier *notifier;
> +
> +	RTE_LOG(DEBUG, EAL, "Released lcore %u.\n", lcore_id);
> +	rte_spinlock_lock(&lcore_notifiers_lock);
> +	TAILQ_FOREACH_REVERSE(notifier, &lcore_notifiers, lcore_notifiers_head,
> +			next) {
> +		notifier->cb(lcore_id, RTE_LCORE_EVENT_RELEASE_EXTERNAL,
> +			notifier->arg);
> +	}
> +	rte_spinlock_unlock(&lcore_notifiers_lock);
> +}
> diff --git a/lib/librte_eal/common/eal_common_thread.c b/lib/librte_eal/common/eal_common_thread.c
> index a81b192ff3..f66d1ccaef 100644
> --- a/lib/librte_eal/common/eal_common_thread.c
> +++ b/lib/librte_eal/common/eal_common_thread.c
> @@ -285,6 +285,12 @@ rte_thread_register(void)
>  
>  	rte_thread_init(lcore_id, &cpuset);
>  
> +	if (lcore_id != LCORE_ID_ANY &&
> +			eal_lcore_external_notify_allocated(lcore_id) < 0) {
> +		eal_lcore_external_release(lcore_id);
> +		RTE_PER_LCORE(_lcore_id) = lcore_id = LCORE_ID_ANY;
> +	}
> +
>  	RTE_LOG(DEBUG, EAL, "Registered thread as lcore %u.\n", lcore_id);
>  	RTE_PER_LCORE(thread_registered) = true;
>  }
> @@ -298,8 +304,11 @@ rte_thread_unregister(void)
>  		return;
>  
>  	lcore_id = RTE_PER_LCORE(_lcore_id);
> -	if (lcore_id != LCORE_ID_ANY)
> +	if (lcore_id != LCORE_ID_ANY) {
> +		eal_lcore_external_notify_removed(lcore_id);
>  		eal_lcore_external_release(lcore_id);
> +		RTE_PER_LCORE(_lcore_id) = LCORE_ID_ANY;
> +	}
>  
>  	rte_thread_uninit();
>  
> diff --git a/lib/librte_eal/common/eal_private.h b/lib/librte_eal/common/eal_private.h
> index 8dd850f68a..649697c368 100644
> --- a/lib/librte_eal/common/eal_private.h
> +++ b/lib/librte_eal/common/eal_private.h
> @@ -283,6 +283,21 @@ uint64_t get_tsc_freq_arch(void);
>   */
>  unsigned int eal_lcore_external_reserve(void);
>  
> +/**
> + * Evaluate all lcore notifiers with a RTE_LCORE_EVENT_NEW_EXTERNAL event for
> + * the passed lcore.
> + * If an error is returned by one of them, then this change is rolled back:
> + * all previous lcore notifiers that had acked the RTE_LCORE_EVENT_NEW_EXTERNAL
> + * event receive a RTE_LCORE_EVENT_RELEASE_EXTERNAL event for the passed lcore.
> + *
> + * @param lcore_id
> + *   The lcore to consider.
> + * @return
> + *   - 0 if all notifiers agreed on the new lcore
> + *   - -1 if one of them refused
> + */
> +int eal_lcore_external_notify_allocated(unsigned int lcore_id);
> +
>  /**
>   * Release an external lcore.
>   *
> @@ -291,6 +306,17 @@ unsigned int eal_lcore_external_reserve(void);
>   */
>  void eal_lcore_external_release(unsigned int lcore_id);
>  
> +/**
> + * Evaluate all lcore notifiers with a RTE_LCORE_EVENT_RELEASE_EXTERNAL event
> + * for the passed lcore.
> + * This function must be called with a lcore that successfully passed
> + * eal_lcore_external_notify_allocated().
> + *
> + * @param lcore_id
> + *   The lcore with role ROLE_EXTERNAL to release.
> + */
> +void eal_lcore_external_notify_removed(unsigned int lcore_id);
> +
>  /**
>   * Prepare physical memory mapping
>   * i.e. hugepages on Linux and
> diff --git a/lib/librte_eal/include/rte_lcore.h b/lib/librte_eal/include/rte_lcore.h
> index 9cf34efef4..e0fec33d5a 100644
> --- a/lib/librte_eal/include/rte_lcore.h
> +++ b/lib/librte_eal/include/rte_lcore.h
> @@ -238,6 +238,55 @@ __rte_experimental
>  void
>  rte_lcore_dump(FILE *f);
>  
> +enum rte_lcore_event_type {
> +	RTE_LCORE_EVENT_NEW_EXTERNAL,
> +	RTE_LCORE_EVENT_RELEASE_EXTERNAL,
> +};
> +
> +/**
> + * Callback prototype for getting lcore events.
> + *
> + * @param lcore_id
> + *   The lcore to consider for this event.
> + * @param event
> + *   The type of event on the lcore.
> + * @param arg
> + *   An opaque pointer passed at notifier registration.
> + * @return
> + *   - -1 when refusing this event,
> + *   - 0 otherwise.
> + */
> +typedef int (*rte_lcore_notifier_cb)(unsigned int lcore_id,
> +	enum rte_lcore_event_type event, void *arg);
> +
> +/**
> + * Register a lcore notifier.
> + *
> + * @param cb
> + *   The callback invoked for each lcore event with the arg argument.
> + *   See rte_lcore_notifier_cb description.
> + * @param arg
> + *   An optional argument that gets passed to the callback when it gets
> + *   invoked.
> + * @return
> + *   On success, returns an opaque pointer for the created notifier.
> + *   NULL on failure.
> + */
> +__rte_experimental
> +void *
> +rte_lcore_notifier_register(rte_lcore_notifier_cb cb, void *arg);
> +
> +/**
> + * Unregister a lcore notifier.
> + *
> + * @param handle
> + *   The handle pointer returned by a former successful call to
> + *   rte_lcore_notifier_register.
> + */
> +__rte_experimental
> +void
> +rte_lcore_notifier_unregister(void *handle);
> +
>  /**
>   * Set core affinity of the current thread.
>   * Support both EAL and non-EAL thread and update TLS.
> diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
> index 6754d52543..1e6f2aaacc 100644
> --- a/lib/librte_eal/rte_eal_version.map
> +++ b/lib/librte_eal/rte_eal_version.map
> @@ -396,6 +396,8 @@ EXPERIMENTAL {
>  
>  	# added in 20.08
>  	rte_lcore_dump;
> +	rte_lcore_notifier_register;
> +	rte_lcore_notifier_unregister;
>  	rte_thread_register;
>  	rte_thread_unregister;
>  };