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

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

> -----Original Message-----
> From: Neil Horman [mailto:nhorman@tuxdriver.com]
> Sent: Wednesday, October 8, 2014 8:16 PM
> To: Pattan, Reshma
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH RFC] librte_reorder: new reorder library
> 
> 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?
> 
Sequence number marking can be done in  either of these places  1)PMD rx side 2)  packet distributor process  or 3) in application itself.

Thanks,
Reshma

> Neil