[dpdk-dev] [PATCH RFC] librte_reorder: new reorder library

["Pattan, Reshma" <reshma.pattan@intel.com>]

Hi All,

I am planning  to implement packet reorder library. Details are as below, please go through them and provide the comments.

Requirement:
               To reorder out of ordered packets that are received from different cores.

Usage:
To be used along with distributor library. Next version of distributor are planned to distribute incoming packets to all worker cores irrespective of the flow type.
In this case to ensure in order delivery of the packets at output side reorder library will used by the tx end.

Assumption:
All input packets will be marked with sequence number in seqn field of mbuf, this will be the reference for reordering at the tx end.
Sequence number will be of type uint32_t. New sequence number field seqn will be added to mbuf structure.

Design:
a)There will be reorder buffer(circular buffer) structure maintained in reorder library to store reordered packets and other details of buffer like head to drain the packet from, min sequence number and other details.
               b)Library will provide insert and drain functions to reorder and fetch out the reordered packets respectively.
c)Users of library should pass the packets to insert functions for reordering.

Insertion logic:
Sequence number of current packet will be used to calculate offset in reorder buffer and write packet to the location  in the reorder buffer corresponding to offset.
                             Offset is calculated as difference of current packet  sequence number and sequence number associated with  reorder buffer.

During sequence number wrapping or wrapping over of reorder buffer size, before inserting the new packet we should move offset number of packets to other buffer called overflow buffer and advance the head of reorder buffer by "offset-reorder buffer size" and insert the new packet.

Insert function:
int rte_reorder_insert(struct rte_reorder_buffer *buffer, struct rte_mbuf *mbuf);
Note: Other insert function is also under plan to insert burst of packets.

               Reorder buffer:
struct rte_reorder_buffer {
        unsigned int size;      /* The size (number of entries) of the buffer. */
        unsigned int mask;      /* Mask (size - 1) of the buffer */
        unsigned int head;      /* Current head of buffer */
        uint32_t min_seqn;      /* latest sequence number associated with buffer */
        struct rte_mbuf *entries[MAX_REORDER_BUFFER_SIZE]; /* buffer to hold reordered mbufs */
};

d)Users can fetch out the reordered packets by drain function provided by library. Users must pass the mbuf array , drain function should fill  passed mbuff array  with the reordered buffer packets.
During drain operation, overflow buffer  packets will be fetched out first and then reorder buffer.

Drain function:
               int rte_reorder_drain(struct rte_reorder_buffer *buffer, struct rte_mbuf **mbufs)

Thanks,
Reshma

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