RE: [RFC] dmadev: add QoS capability

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Vamsi Attunuru [mailto:vattunuru@marvell.com]
> Sent: Monday, 29 July 2024 13.56
> 
> Some DMA controllers support QoS at HW command queue level to
> differentiate the performance on different HW queues based on
> the priority configured. Patch adds required fields in dmadev
> structures to get hardware supported priority levels and the
> provision to configure the priority from the applications.

Do we foresee anything more advanced than Strict Priority scheduling for DMA anytime in the future?

If not, then consider calling this new capability Prioritization (CAPA_PRIO) instead of Quality Of Service (CAPA_QOS). Then we don't need to add and describe QoS parameters for a more advanced QoS scheduling algorithm (e.g. the "weight" for weighted fair queueing).

> 
> Signed-off-by: Vamsi Attunuru <vattunuru@marvell.com>
> ---
>  lib/dmadev/rte_dmadev.c | 10 ++++++++++
>  lib/dmadev/rte_dmadev.h | 19 +++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/lib/dmadev/rte_dmadev.c b/lib/dmadev/rte_dmadev.c
> index 845727210f..9ff62efcb4 100644
> --- a/lib/dmadev/rte_dmadev.c
> +++ b/lib/dmadev/rte_dmadev.c
> @@ -491,6 +491,16 @@ rte_dma_configure(int16_t dev_id, const struct
> rte_dma_conf *dev_conf)
>  			"Device %d configure too many vchans", dev_id);
>  		return -EINVAL;
>  	}
> +	if (dev_conf->priority &&

-	if (dev_conf->priority &&
+ 	if (dev_conf->priority != 0 &&

> +	    !(dev_info.dev_capa & RTE_DMA_CAPA_QOS)) {
> +		RTE_DMA_LOG(ERR, "Device %d don't support QoS", dev_id);
> +		return -EINVAL;
> +	}
> +	if (dev_conf->priority >= dev_info.nb_priorities) {
> +		RTE_DMA_LOG(ERR,
> +			"Device %d configure invalid priority", dev_id);
> +		return -EINVAL;
> +	}
>  	if (dev_conf->enable_silent &&
>  	    !(dev_info.dev_capa & RTE_DMA_CAPA_SILENT)) {
>  		RTE_DMA_LOG(ERR, "Device %d don't support silent", dev_id);
> diff --git a/lib/dmadev/rte_dmadev.h b/lib/dmadev/rte_dmadev.h
> index 5474a5281d..08db8ead0a 100644
> --- a/lib/dmadev/rte_dmadev.h
> +++ b/lib/dmadev/rte_dmadev.h
> @@ -268,6 +268,16 @@ int16_t rte_dma_next_dev(int16_t start_dev_id);
>  #define RTE_DMA_CAPA_OPS_COPY_SG	RTE_BIT64(33)
>  /** Support fill operation. */
>  #define RTE_DMA_CAPA_OPS_FILL		RTE_BIT64(34)
> +/** Support QoS at DMA HW channel level
> + *
> + * If device supports QoS then application could configure priority to the
> + * DMA HW channel using 'priority' field in struct rte_dma_conf. Number of
> + * supported prioirty levels will be known from 'nb_priorities' field in
> + * struct rte_dma_info.
> + * DMA devices which support QoS at HW channel level can advertise this
> + * capability.
> + */
> +#define RTE_DMA_CAPA_QOS		RTE_BIT64(35)
>  /**@}*/
> 
>  /**
> @@ -297,6 +307,8 @@ struct rte_dma_info {
>  	int16_t numa_node;
>  	/** Number of virtual DMA channel configured. */
>  	uint16_t nb_vchans;
> +	/** Number of priority levels supported by DMA HW channel. */
> +	uint16_t nb_priorities;

This value must be 0 or > 1, never 1. Please mention in the comment, e.g.:

/** Number of priority levels, if supported by DMA HW channel. 0 otherwise. */

Please add a test case to verify that the DMA device reports nb_priorities > 1 if it has CAPA_PRIO, and 0 if not.
Alternatively:
Assuming we don't foresee anything more advanced than Strict Priority...
Remove the CAPA_PRIO capability flag. Reading nb_priorities should suffice.

>  };
> 
>  /**
> @@ -332,6 +344,13 @@ struct rte_dma_conf {
>  	 * @see RTE_DMA_CAPA_SILENT
>  	 */
>  	bool enable_silent;
> +	/* The prioirty of the DMA HW channel.
> +	 * This value cannot be greater than or equal to the field
> 'nb_priorities'
> +	 * of struct rte_dma_info which get from rte_dma_info_get().
> +	 * Among the values between '0' and 'nb_priorities - 1', lowest value
> +	 * indicates higher priority and vice-versa.
> +	 */
> +	uint16_t priority;
>  };
> 
>  /**
> --
> 2.25.1