Re: [dpdk-dev] [PATCH v3 2/8] dmadev: add burst capacity API

[Jerin Jacob <jerinjacobk@gmail.com>]

On Tue, 7 Sep 2021, 10:25 pm Bruce Richardson, <bruce.richardson@intel.com>
wrote:

> From: Kevin Laatz <kevin.laatz@intel.com>
>
> Add a burst capacity check API to the dmadev library. This API is useful to
> applications which need to how many descriptors can be enqueued in the
> current batch. For example, it could be used to determine whether all
> segments of a multi-segment packet can be enqueued in the same batch or not
> (to avoid half-offload of the packet).
>

 #Could you share more details on the use case with vhost?
# Are they planning to use this in fast path if so it need to move as fast
path function pointer?
# Assume the use case needs N rte_dma_copy to complete a logical copy at
vhost level. Is the any issue in half-offload, meaning when N th one
successfully completed then only the logical copy is completed. Right?
# There is already nb_desc with which a dma_queue is configured. So if the
application does its accounting properly, it knows how many desc it has
used up and how many completions it has processed.

Would like to understand more details on this API usage.

Sorry for the format issue, sending from mobile.


> Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
> ---
>  lib/dmadev/rte_dmadev.c      | 11 +++++++++++
>  lib/dmadev/rte_dmadev.h      | 19 +++++++++++++++++++
>  lib/dmadev/rte_dmadev_core.h |  5 +++++
>  lib/dmadev/version.map       |  1 +
>  4 files changed, 36 insertions(+)
>
> diff --git a/lib/dmadev/rte_dmadev.c b/lib/dmadev/rte_dmadev.c
> index ab45928efb..6494871f05 100644
> --- a/lib/dmadev/rte_dmadev.c
> +++ b/lib/dmadev/rte_dmadev.c
> @@ -573,6 +573,17 @@ dmadev_dump_capability(FILE *f, uint64_t dev_capa)
>         fprintf(f, "\n");
>  }
>
> +int
> +rte_dmadev_burst_capacity(uint16_t dev_id, uint16_t vchan)
> +{
> +       const struct rte_dmadev *dev = &rte_dmadevices[dev_id];
> +
> +       RTE_DMADEV_VALID_DEV_ID_OR_ERR_RET(dev_id, -EINVAL);
> +
> +       RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->burst_capacity, -ENOTSUP);
> +       return (*dev->dev_ops->burst_capacity)(dev, vchan);
> +}
> +
>  int
>  rte_dmadev_dump(uint16_t dev_id, FILE *f)
>  {
> diff --git a/lib/dmadev/rte_dmadev.h b/lib/dmadev/rte_dmadev.h
> index 39d73872c8..8b84914810 100644
> --- a/lib/dmadev/rte_dmadev.h
> +++ b/lib/dmadev/rte_dmadev.h
> @@ -673,6 +673,25 @@ __rte_experimental
>  int
>  rte_dmadev_vchan_status(uint16_t dev_id, uint16_t vchan, enum
> rte_dmadev_vchan_status *status);
>
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Check remaining capacity in descriptor ring for the current burst.
> + *
> + * @param dev_id
> + *   The identifier of the device.
> + * @param vchan
> + *   The identifier of virtual DMA channel.
> + *
> + * @return
> + *   - Remaining space in the descriptor ring for the current burst on
> success.
> + *   - -ENOTSUP: if not supported by the device.
> + */
> +__rte_experimental
> +int
> +rte_dmadev_burst_capacity(uint16_t dev_id, uint16_t vchan);
> +
>  /**
>   * @warning
>   * @b EXPERIMENTAL: this API may change without prior notice.
> diff --git a/lib/dmadev/rte_dmadev_core.h b/lib/dmadev/rte_dmadev_core.h
> index 3c9d698044..2756936798 100644
> --- a/lib/dmadev/rte_dmadev_core.h
> +++ b/lib/dmadev/rte_dmadev_core.h
> @@ -52,6 +52,10 @@ typedef int (*rte_dmadev_stats_get_t)(const struct
> rte_dmadev *dev,
>  typedef int (*rte_dmadev_stats_reset_t)(struct rte_dmadev *dev, uint16_t
> vchan);
>  /**< @internal Used to reset basic statistics. */
>
> +typedef uint16_t (*rte_dmadev_burst_capacity_t)(const struct rte_dmadev
> *dev,
> +                       uint16_t vchan);
> +/** < @internal Used to check the remaining space in descriptor ring. */
> +
>  typedef int (*rte_dmadev_dump_t)(const struct rte_dmadev *dev, FILE *f);
>  /**< @internal Used to dump internal information. */
>
> @@ -114,6 +118,7 @@ struct rte_dmadev_ops {
>         rte_dmadev_stats_get_t      stats_get;
>         rte_dmadev_stats_reset_t    stats_reset;
>
> +       rte_dmadev_burst_capacity_t burst_capacity;
>         rte_dmadev_vchan_status_t   vchan_status;
>
>         rte_dmadev_dump_t           dev_dump;
> diff --git a/lib/dmadev/version.map b/lib/dmadev/version.map
> index 10eeb0f7a3..56cb279e8f 100644
> --- a/lib/dmadev/version.map
> +++ b/lib/dmadev/version.map
> @@ -1,6 +1,7 @@
>  EXPERIMENTAL {
>         global:
>
> +       rte_dmadev_burst_capacity;
>         rte_dmadev_close;
>         rte_dmadev_completed;
>         rte_dmadev_completed_status;
> --
> 2.30.2
>
>