Re: [dpdk-dev] [PATCH 1/3] eventdev: introduce adapter flags for periodic mode

["Carrillo, Erik G" <erik.g.carrillo@intel.com>]

Hi Shijith,

Some comments in-line:

> -----Original Message-----
> From: Shijith Thotton <sthotton@marvell.com>
> Sent: Monday, March 8, 2021 2:46 PM
> To: Carrillo, Erik G <erik.g.carrillo@intel.com>
> Cc: Shijith Thotton <sthotton@marvell.com>; Pavan Nikhilesh
> <pbhagavatula@marvell.com>; Jerin Jacob <jerinj@marvell.com>;
> dev@dpdk.org
> Subject: [PATCH 1/3] eventdev: introduce adapter flags for periodic mode
> 
> A timer adapter in periodic mode can be used to arm periodic timers.
> This patch adds flags used to advertise capability and configure timer adapter
> in periodic mode. Capability flag should be set for adapters which support
> periodic mode.
> 
> Below is a programming sequence on the usage:
> 	/* check for periodic mode support by reading capability. */
> 	rte_event_timer_adapter_caps_get(...);
> 
> 	/* create adapter in periodic mode by setting periodic flag
> 	   (RTE_EVENT_TIMER_ADAPTER_F_PERIODIC) and resolution. */
> 	rte_event_timer_adapter_create_ext(...);
> 
> 	/* arm periodic timer of configured resolution */
> 	rte_event_timer_arm_burst(...);
> 
> 	/* timer event will be periodically generated at configured
> 	   resolution till cancel is called. */
> 	while (running) { rte_event_dequeue_burst(...); }
> 
> 	/* cancel periodic timer which stops generating events */
> 	rte_event_timer_cancel_burst(...);
> 
> Signed-off-by: Shijith Thotton <sthotton@marvell.com>
> ---
>  doc/guides/prog_guide/event_timer_adapter.rst | 33
> +++++++++++++++++++  lib/librte_eventdev/rte_event_timer_adapter.h |
> 6 ++++
>  lib/librte_eventdev/rte_eventdev.h            |  3 ++
>  3 files changed, 42 insertions(+)
> 
> diff --git a/doc/guides/prog_guide/event_timer_adapter.rst
> b/doc/guides/prog_guide/event_timer_adapter.rst
> index a95efbe0d..fcdecdb3b 100644
> --- a/doc/guides/prog_guide/event_timer_adapter.rst
> +++ b/doc/guides/prog_guide/event_timer_adapter.rst
> @@ -252,6 +252,39 @@ be canceled by calling
> ``rte_event_timer_cancel_burst()``:
>           */
>  	rte_event_timer_cancel_burst(adapter, &conn->timer, 1);
> 
> +Timer adapter in periodic mode
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +A periodic timer is a timer, which expires at fixed time intervals
> +continuously till it is cancelled.  A timer adapter can be configured
> +to arm such timers by configuring it in periodic mode.  Capability flag
> +``RTE_EVENT_TIMER_ADAPTER_CAP_PERIODIC`` can be used to check if an
> +adapter supports periodic mode. An adapter in periodic mode can only be
> +used to arm periodic timers.
> +
> +Example config to create an adapter in periodic mode with 100ms
> resolution:
> +
> +.. code-block:: c
> +
> +	#define NSECPERSEC 1E9 // No of ns in 1 sec
> +	const struct rte_event_timer_adapter_conf adapter_config = {
> +                .event_dev_id = event_dev_id,
> +                .timer_adapter_id = 0,
> +                .clk_src = RTE_EVENT_TIMER_ADAPTER_CPU_CLK,
> +                .timer_tick_ns = NSECPERSEC / 10, // 100 milliseconds
> +                .nb_timers = 100,
> +                .timer_adapter_flags = RTE_EVENT_TIMER_ADAPTER_F_PERIODIC,
> +	};
> +
> +``timer_adapter_flags`` is set to include periodic flag
> +``RTE_EVENT_TIMER_ADAPTER_F_PERIODIC`` and ``timer_tick_ns`` to
> resolution.
> +Maximum timeout (``max_tmo_nsec``) does not apply for periodic mode.

This content can be reworked slightly and moved into the "Create and Configure an Adapter Instance" section, perhaps as a subsection describing the two adapter modes.

> +
> +After starting the adapter, event timer arm APIs can be used to arm
> +periodic timers.  Timer events will be generated at configured
> +``timer_tick_ns`` intervals.  Event generation can be stopped using
> +cancel API ``rte_event_timer_cancel_burst``.
> +

I think this content should be worked into the "Arming Event Timers" section, indicating how the timer behavior depends on the mode of the adapter that specified in the arm call.

>  Processing Timer Expiry Events
>  ------------------------------
> 
> diff --git a/lib/librte_eventdev/rte_event_timer_adapter.h
> b/lib/librte_eventdev/rte_event_timer_adapter.h
> index d2ebcb090..f9fc95711 100644
> --- a/lib/librte_eventdev/rte_event_timer_adapter.h
> +++ b/lib/librte_eventdev/rte_event_timer_adapter.h

I think we should also update the doxygen documentation for the rte_event_timer_arm_burst to indicate that timer expiry events will be generated once or periodically until the timer is stopped based on the mode of the adapter that is specified.  We can have a "see also" for the RTE_EVENT_TIMER_ADAPTER_F_PERIODIC flag.

Thanks,
Erik

> @@ -151,6 +151,12 @@ enum rte_event_timer_adapter_clk_src {
>   * @see struct rte_event_timer_adapter_conf::flags
>   */
> 
> +#define RTE_EVENT_TIMER_ADAPTER_F_PERIODIC	(1ULL << 2)
> +/**< Flag to configure event timer adapter in periodic mode.
> + *
> + * @see struct rte_event_timer_adapter_conf::flags
> + */
> +
>  /**
>   * Timer adapter configuration structure
>   */