Re: [dpdk-dev] [RFC] ethdev: add new fields for max LRO session size

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: Yigit, Ferruh
> Sent: Friday, October 18, 2019 5:36 PM
> To: Thomas Monjalon <thomas@monjalon.net>; Matan Azrad <matan@mellanox.com>
> Cc: dev@dpdk.org; Andrew Rybchenko <arybchenko@solarflare.com>; Ananyev, Konstantin <konstantin.ananyev@intel.com>; Olivier Matz
> <olivier.matz@6wind.com>
> Subject: Re: [RFC] ethdev: add new fields for max LRO session size
> 
> On 10/2/2019 2:58 PM, Thomas Monjalon wrote:
> > 24/09/2019 14:03, Matan Azrad:
> >> From: Ferruh Yigit
> >>> On 9/15/2019 8:48 AM, Matan Azrad wrote:
> >>>> Hi Ferruh
> >>>>
> >>>> From: Ferruh Yigit <ferruh.yigit@intel.com>
> >>>>> On 8/29/2019 8:47 AM, Matan Azrad wrote:
> >>>>>> It may be needed by the user to limit the LRO session packet size.
> >>>>>> In order to allow the above limitation, add new Rx configuration for
> >>>>>> the maximum LRO session size.
> >>>>>>
> >>>>>> In addition, Add a new capability to expose the maximum LRO session
> >>>>>> size supported by the port.
> >>>>>>
> >>>>>> Signed-off-by: Matan Azrad <matan@mellanox.com>
> >>>>>
> >>>>> Hi Matan,
> >>>>>
> >>>>> Is there any existing user of this new field?
> >>>>
> >>>> All the LRO users need it due to the next reasons:
> >>>>
> >>>> 1. If scatter is enabled - The dpdk user can limit the LRO session size created
> >>> by the HW by this field, if no field like that - there is no way to limit it.
> >>>> 2. No scatter - the dpdk user may want to limit the LRO packet size in order
> >>> to save enough tail-room in the mbuf for its own usage.
> >>>> 3. The limitation of max_rx_pkt_len is not enough - doesn't make sense to
> >>> limit LRO traffic as single packet.
> >>>>
> >>>
> >>> So should there be more complement patches to this RFC? To update the
> >>> users of the field with the new field.
> >>
> >>
> >> We already exposed it as ABI breakage in the last deprecation notice.
> >> We probably cannot complete it for 19.11 version, hopefully for 20.02 it will be completed.
> >
> > We won't break the ABI in 20.02.
> > What should be done in 19.11?
> >
> 
> The ask was to add code that uses new added fields, this patch only adds new
> field to two public ethdev struct.
> 
> @Thomas, @Andrew, if this patch doesn't goes it on this release it will have to
> wait a year. I would like to see the implementation but it is not there, what is
> your comment?

Just a side note, if I am not mistaken, there is a 6B gap in eth_rxmode:

struct rte_eth_rxmode {
	/** The multi-queue packet distribution mode to be used, e.g. RSS. */
	enum rte_eth_rx_mq_mode mq_mode;
	uint32_t max_rx_pkt_len;  /**< Only used if JUMBO_FRAME enabled. */
	uint16_t split_hdr_size;  /**< hdr buf size (header_split enabled).*/   <---- offset 8
	/**
	 * Per-port Rx offloads to be set using DEV_RX_OFFLOAD_* flags.
	 * Only offloads set on rx_offload_capa field on rte_eth_dev_info
	 * structure are allowed to be set.
	 */
	uint64_t offloads;        <--- offset 16
};


So we can reserve these 6B, and then reuse for LRO, or whatever.
Might be it would help somehow.