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

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, Oct 08, 2014 at 02:11:34PM +0000, Pattan, Reshma wrote:
> 
> 
> > -----Original Message-----
> > From: Neil Horman [mailto:nhorman@tuxdriver.com]
> > Sent: Tuesday, October 7, 2014 12:22 PM
> > To: Pattan, Reshma
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH RFC] librte_reorder: new reorder library
> > 
> > On Tue, Oct 07, 2014 at 09:33:06AM +0000, Pattan, Reshma wrote:
> > > 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
> > >
> > 
> > This seems reasonable, but why not integrate it with the distributor library rather
> > than create a separate library for it?  It seems as though the distributor library is
> > a pre-requisite for this libraries use anyway, as otherwise there will not be
> > anything to reorder Neil
> > 
> 
> Hi  Neil,
> 
> Reorder library should be standalone , as there are many ways that can cause out of ordering of packets, I just mentioned future packet distributor enhancements 
>  as one of the example for out of ordering. 
> Other ways like, users can directly distribute the packets to different cores via rings and that causes packet out of ordering as well. 
> So, keeping reorder library standalone would be good to work with all packet distribution ways.
> 


Hmm, ok, that seems reasonable.

Just out of curiosity, where do you intend to inject the packet sequence number
for this library?

Neil