[dpdk-dev] [PATCH v2 4/4] doc: new reorder library description

Iremonger, Bernard bernard.iremonger at intel.com
Mon Feb 2 13:18:32 CET 2015



> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Sergio Gonzalez Monroy
> Sent: Friday, January 30, 2015 1:15 PM
> To: dev at dpdk.org
> Subject: [dpdk-dev] [PATCH v2 4/4] doc: new reorder library description
> 
> This patch introduces a new section in the programmers guide describing the reorder library.
> 
> Signed-off-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy at intel.com>
> ---
>  doc/guides/prog_guide/index.rst       |   1 +
>  doc/guides/prog_guide/reorder_lib.rst | 110 ++++++++++++++++++++++++++++++++++
>  2 files changed, 111 insertions(+)
>  create mode 100644 doc/guides/prog_guide/reorder_lib.rst
> 
> diff --git a/doc/guides/prog_guide/index.rst b/doc/guides/prog_guide/index.rst index
> 8d86dd4..de69682 100644
> --- a/doc/guides/prog_guide/index.rst
> +++ b/doc/guides/prog_guide/index.rst
> @@ -61,6 +61,7 @@ Programmer's Guide
>      lpm_lib
>      lpm6_lib
>      packet_distrib_lib
> +    reorder_lib
>      ip_fragment_reassembly_lib
>      multi_proc_support
>      kernel_nic_interface
> diff --git a/doc/guides/prog_guide/reorder_lib.rst b/doc/guides/prog_guide/reorder_lib.rst
> new file mode 100644
> index 0000000..558804d
> --- /dev/null
> +++ b/doc/guides/prog_guide/reorder_lib.rst
> @@ -0,0 +1,110 @@
> +..  BSD LICENSE
> +    Copyright(c) 2010-2015 Intel Corporation. All rights reserved.

Hi Sergio,
"2010-2015" should be change to "2015" as this is a new file.

> +    All rights reserved.
> +
> +    Redistribution and use in source and binary forms, with or without
> +    modification, are permitted provided that the following conditions
> +    are met:
> +
> +    * Redistributions of source code must retain the above copyright
> +    notice, this list of conditions and the following disclaimer.
> +    * Redistributions in binary form must reproduce the above copyright
> +    notice, this list of conditions and the following disclaimer in
> +    the documentation and/or other materials provided with the
> +    distribution.
> +    * Neither the name of Intel Corporation nor the names of its
> +    contributors may be used to endorse or promote products derived
> +    from this software without specific prior written permission.
> +
> +    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> +    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> +    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
> +    A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
> +    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> +    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> +    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
> +    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
> +    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> +    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
> +    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> +
> +.. _Reorder_Library:
> +
> +Reorder Library
> +=================
> +
> +The Reorder Library provides a mechanism for reordering mbufs based on
> +their sequence number.
> +
> +Operation
> +----------
> +
> +The reorder library is essentially a buffer that reorders mbufs.
> +The user inserts out of order mbufs into the reorder buffer and pulls
> +ordered mbufs from it.
> +
> +At a given time, the reorder buffer contains mbufs whose sequence
> +number are inside the sequence window. The sequence window is
> +determined by the minimum sequence number and the number of entries that the buffer was
> configured with.
> +As an example, given a reorder buffer with 200 entries and a minimum
> +sequence number of 350, the sequence window has high and low limits of
> +550 and 350 respectively.
> +
> +When inserting mbufs, the reorder library differentiates between valid,
> +early and late mbufs depending on the sequence number of the inserted mbuf:
> +
> +* valid: the sequence number is inside the window.
> +* late: the sequence number is outside the window and less than the low limit.
> +* early: the sequence number is outside the window and greater than the
> +high
> +  limit.
> +
> +The reorder buffer directly returns late mbufs and tries to allocate
> +early mbufs.
> +
> +
> +Implementation Details
> +-------------------------
> +
> +The reorder library is implemented as a double buffer, which we will
> +refer to as the *Order* buffer and the *Ready* buffer.
> +
> +Valid mbufs are inserted directly into the Order buffer and late mbufs
> +are returned to the user.
> +
> +In the case of early mbufs, the reorder buffer will try to move the
> +window (incrementing the minimum sequence number) so that the mbuf becomes a valid one.
> +To that end, mbufs in the Order buffer are moved into the Ready buffer.
> +Any mbufs that have not arrived yet are ignored and therefore will
> +become late mbufs.
> +This means that as long as there is room in the Ready buffer, the
> +window will be moved to accommodate early mbufs.
> +
> +For example, assuming that we have a buffer of 200 entries with a 350
> +minimum sequence number, and we need to insert an early mbuf with 565 sequence number.
> +That means that we would need to move the windows at least 15 positions
> +to accommodate the mbuf.
> +The reorder buffer would try to move at least 15 mbufs from the Order
> +to the Ready buffer, as long as there is room in the Ready buffer.
> +
> +When draining mbufs, the reorder buffer would return  mbufs in the
> +Ready buffer first and then from the Order buffer until a gap is found
> +(mbufs that have not arrived yet).
> +
> +Use Case: Packet Distributor
> +-------------------------------
> +
> +An application using the DPDK packet distributor could make use of the
> +reorder library to transmit packets in the same order they were received.
> +
> +A basic packet distributor use case would consist of a distributor core
> +with multiple workers.
> +The processing of packets by the workers is not guaranteed to be in
> +order, hence a reorder buffer can be used to order as many packets as possible.
> +
> +In such a scenario, the distributor assigns a sequence number to mbufs
> +before delivering them to the workers.
> +As the workers finish processing the packets, the distributor inserts
> +those mbufs into the reorder buffer and finally transmit drained mbufs.
> +
> +Currently the reorder buffer is not thread safe so the same thread is
> +responsible for inserting and draining mbufs.
> --
> 1.9.3
Regards,

Bernard.


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