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TSVWG                                                          Y. Zhuang
Internet-Draft                                                  R. Huang
Intended status: Informational             Huawei Technologies Co., Ltd.
Expires: January 5, 2020                                    July 4, 2019


  An Open Congestion Control Architecture with network cooperation for
                              RDMA Fabric
                  draft-zhh-tsvwg-open-architecture-00

Abstract

   This document describes an open congestion control architecture with
   network cooperation (including network proactive and passive control)
   for high performance RDMA fabric to provide low latency and high
   throughput for datacenter applications such as the AI computing.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 5, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Abbreviations . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Design Principle for high performance RDMA fabric . . . . . .   3
   5.  Architecture Overview . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Roles and Functionalities . . . . . . . . . . . . . . . .   6
       5.1.1.  Sender NIC  . . . . . . . . . . . . . . . . . . . . .   6
       5.1.2.  Switch  . . . . . . . . . . . . . . . . . . . . . . .   6
       5.1.3.  Receiver NIC  . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Interfaces  . . . . . . . . . . . . . . . . . . . . . . .   7
       5.2.1.  NIC interfaces  . . . . . . . . . . . . . . . . . . .   8
       5.2.2.  Network interface . . . . . . . . . . . . . . . . . .   8
   6.  Compatibility Consideration . . . . . . . . . . . . . . . . .   9
     6.1.  Negotiate the congestion control capability . . . . . . .   9
     6.2.  Co-exist with current NIC to NIC control channel  . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Manageability Consideration . . . . . . . . . . . . . . . . .  10
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Traditionally, RDMA (Remote Direct Memory Access) is running over the
   closed and expensive InfiniBand (IB) [IB] networks.  However, due to
   the limitation of network scalability and high costs of IB, RDMA
   traffic is moving to IP/Ethernet as its underlay networks for better
   scale and low cost.  Supporting RDMA over IP/Ethernet using lower
   price NICs and Switches with reduced latency is important for low
   latency and high throughput datacenter applications such as AI
   Computing.

   As such, the datacenter networks (DCNs) nowadays is not only
   providing traffic transmission for tenants using TCP/IP network
   protocol stack, but also is required to provide RDMA traffic for High
   Performance Computing (HPC) and distributed storage accessing
   applications which requires low latency and high throughput.  With
   that said, there are more stringent requirements for basic
   performance of DCN.

   [Requirement] discusses major problems of current RDMA fabric
   technologies and the requirements for better performance.  Also,
   [HPC] presents the problems of current RDMA fabric from a cloud
   operators' perspectives.Based on that, this document proposes an open



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   congestion control architecture of hosts and networks with network
   cooperation (including network proactive and passive control) for the
   high performance RDMA fabric to provide better congestion control.

   The scalability and compatibility of congestion control under the
   proposed architecture are also discussed in order to provide
   incremental upgrade of the current RDMA technologies.

   Discussions of new congestion control algorithms and improved active
   queue management (AQM) are out of scope for this document.

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Abbreviations

      IB - InfinitBand

      HPC - High Performance Computing

      ECN - Explicit Congestion Notification

      AI/HPC - Artificial Intelligence/High-Performance computing

      RDMA - Remote Direct Memory Access

      NIC - Network Interface Card

      AQM - Active Queue Management

      NP - Notification Point

      CP - Congestion Point

      RP - Reaction Point

4.  Design Principle for high performance RDMA fabric

   Based on the [Requirement] and [HPC], the architecture design should
   follow some principles:






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   o  Can adopt enhancements to provide better performance than existing
      technologies, such as better latency, convergence and handling of
      packet loss.

   o  Can support both RoCEv2 and iWARP [RFC5040] as RDMA transports.

   o  Can support mixture of RDMA traffics and normal TCP traffics.

   o  Can provide better interoperability between vendors while keep
      flexibility.

   o  Do not modify or provide limited modification to RDMA data plane.

   o  Be compatible with legacy devices.

   o  Be easy to deploy new congestion control algorithms.

5.  Architecture Overview

   The architecture is shown in Figure 1.  It composes of hosts (i.e.
   sender/receiver NICs) and network nodes (i.e. switches).






























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  Sender(RP)                                           Receiver(NP)

''''''''''''''''''''''''''                            ''''''''''''''''''''''''''
'   +---+  +---+         '                            '    +---+  +---+        '
'   |CC1|  |CC1| ...     '                            '    |CC1|  |CC1| ...    '
'   +-*-+  +-*-+         '                            '    +-*-+  +-*-+        '
'     *      *           '                            '      *      *          '
'+----*------*---------+ '                            ' +----*------*---------+'
'|  Congestion control | '      Switch(CP and NP)     ' |  Congestion control |'
'|  Engine             | '                            ' |  Engine             |'
'+---------------------+ '      '''''''''''''''''     ' +---------------------+'
'+--------++-----------+ '      ' +-----------+ '     ' +-----------++--------+'
'|rate-co ||net-control|<-------- |net-control| '     ' |net-control||rate-co |'
'|ntrol;  ||           | '      ' |           | '     ' |           ||ntrol;  |'
'|loss-re |+-----------+ '      ' +-----------+ '     ' +-----------+|loss-re |'
'|covery  |+-----------+ '      '               '     ' +-----------+|covery  |'
'|        ||nic-control|<........              <........|nic-control||        |'
'|        ||           | '      '               '     ' |           ||        |'
'+--------++-----------+ '      '               '     ' +-----------++--------+'
'+---------------------+ '      '               '     ' +---------------------+'
'|        data         |========>               ======> |        data         |'
'|                     | '      '               '     ' |                     |'
'+---------------------+ '      '               '     ' +---------------------+'
'                        '      '               '     '                        '
''''''''''''''''''''''''''      '''''''''''''''''     ''''''''''''''''''''''''''


<-------- Net2Nic control channel   ========> RDMA stream
<........ Nic2Nic control channel   ********  System APIs

   Figure 1. The open congestion control architecture with network cooperation

   Sender and Receiver are both NICs.  Within the architecture, the NICs
   are proposed to introduce two new interfaces: 1) an interface for the
   operators to install/manage congestion control algorithms which can
   share the local transmit function blocks such as rate control and
   loss recovery to facilitate the deployment of new congestion control
   algorithms and the management of different algorithms while
   regardless of the detailed hardware implementation; 2) an interface
   for net-control module inside network nodes (e.g. switches) to signal
   back to senders, and further incorporate the collected information
   into the local transmit control.

   For the interface to network nodes, we introduce a new NET to NIC
   control channel, in which the control message is initiated and sent
   by the net-control module inside a switch instead of the receiver.
   Since most congestion happens on network nodes, the switch noted as
   congestion point (CP) in Fig.1 should be the point aware of the on-



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   going or expected congestion.  The advantage of doing so, is to
   provide more accurate congestion information and how to prevent or
   resolve the congestion based on traffic traversing and resources
   allocated on the network nodes directly.

   The NIC to NIC control channel signaled by dotted link presents a
   logical channel for legacy NIC to NIC control notification.  It can
   be for example CNP message for RoCEv2 or flags/fields in TCP headers
   for iWARP.  The RDMA data streams is indicated by bold line and works
   as it is.  However, some extensions might be needed to implement the
   new interfaces which is out of the scope for this document.

5.1.  Roles and Functionalities

5.1.1.  Sender NIC

   As the reaction point (RP) of the architecture, the sender NIC can
   deploy/manage the congestion control algorithms based on system
   configurations or the negotiation with remote NICs.  When congestion
   happens, it accordingly adjusts its sending rate based on the used
   congestion control algorithm and signaled feedbacks from both the
   network nodes and/or the receiver's NIC.

5.1.2.  Switch

   Switch is the congestion point, which detects the network congestion
   based on some metrics, such as queue length or measured latency on
   the path or traffic patterns it might have learnt.

   For a legacy switch with ECN enabled, it can mark CE in the IP header
   of RDMA traffics when congestion exists to notify the receivers.
   When the condition is getting worse, it either uses PFC or discard
   the packet based on some AQM policies.  For legacy switches without
   ECN, it discards packets when congestion happens.

   For a switch with net-control module, called a net-control switch
   here, it can act as the notification point (NP) which can initiate
   the control message and delivery it through the NET to NIC control
   channel back to the sender, which adjusts its sending rate
   accordingly.  Net-control switches can be deployed in any places of a
   DCN fabric, e.g., TOR or spine.

5.1.3.  Receiver NIC

   Receiver NIC might negotiate with the sender NIC on the congestion
   control capability.  It is also the notification point (NP).  Based
   on the ECN mark or lost packets, it discovers congestion and send
   congestion information back to the sender through NIC to NIC control



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   channel to adjust sending rate.  In RoCEv2, the CNP message is used
   for the NIC to NIC control.

5.2.  Interfaces

   The architecture introduces two interfaces on NICs and one interface
   on the network node for the open control as shown in Figure 2.  As
   for the NIC, one interface is for deploying/managing different
   congestion controls while the other is to communicate with the
   network control module on switches.  For the switch, the proposed
   interface is dedicated for control of network congestions back to the
   senders.


                          Sender(RP)

                ''''''''''''''''''''''''''
                '   +---+  +---+         '
                '   |CC1|  |CC1| ...     '
                '   +-*-+  +-*-+         '
                '     *      *           '
                '+----*------*---------+ '
                '|  Congestion control | '      Switch(CP and NP)
                '|  Engine             | '
                '+---------------------+ '      '''''''''''''''''
                '+--------++-----------+ '      ' +-----------+ '
                '|rate-co ||net-control|<-------- |net-control| '
                '|ntrol;  ||           | '      ' |           | '
                '|loss-re |+-----------+ '      ' +-----------+ '
                '|covery  |+-----------+ '      '               '
                '|        ||nic-control| '      '
                '|        ||           | '      '               '
                '+--------++-----------+ '      '               '
                '+---------------------+ '      '               '
                '|        data         | '      '
                '|                     | '      '               '
                '+---------------------+ '      '               '
                '                        '      '               '
                ''''''''''''''''''''''''''      '''''''''''''''''

                 <-------- Net2Nic interface   ********  system CC interface

                Figure 2. Imported NIC interfaces and network interface








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5.2.1.  NIC interfaces

   To cope with various scenarios and facilitate the deployment of new
   congestion control algorithms, it would be good if NICs will be able
   to deploy congestion controls and further manage and configure them
   in a common way.  The idea to provide a system CC interface is that
   the cloud operators can deploy/manage congestion control algorithms
   on NICs based on the traffic patterns as well as the network
   resources.  Then the NICs might negotiate the congestion control
   capability with each other.

   The function blocks within in the NIC are logic components, not
   indicating any specific implementation.  A congestion control engine
   acts as a platform to provide a system CC interface to deploy
   different CCs and then map to local actions and communicate with
   local function blocks to provide congestion control operations.

   Ideally, local functions related to congestion controls will be
   implemented as function blocks and interact with each other through
   internal interfaces to achieve the final congestion controls.  As
   such, CCs can share common local operations and it would be easy for
   developers to develop and deploy new CCs regardless of detailed local
   implementations.  The design of the CC Engine and local function
   blocks are out of scope for this document.  An example of the design
   and implantation can be found in [HotCocoa] .

   For now, the local function blocks can include rate-control and loss-
   recovery, as well as two blocks to deal with congestion control
   information from the interface to NIC control and the interface to
   NET control respectively.

   The other proposed interface of the NIC is to the NET control
   (Net2Nic control channel), which is used to collect congestion
   information from the network nodes to be further incorporated to the
   congestion control of sender NICs.

5.2.2.  Network interface

   To achieve more accurate congestion control and ways to prevent or
   resolve the congestion based on traffic traversing, as indicated in
   Figure 2, the net-control switch will provide a network interface
   (Net2Nic interface), by which net-control module inside the node can
   signal back to the senders.

   The definition of Net2Nic control channel messages and processes are
   out of scope for this document.  It relies on the design of net-
   control module which is responsible for dealing with network
   congestions and exposing what precise information to the sender.



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6.  Compatibility Consideration

6.1.  Negotiate the congestion control capability

   The host might negotiate their supported congestion control
   capability during the session setup phase.

   However, it should use the existing way of congestion control as
   default to provide compatibility with legacy devices.

   The net-control switches should be capable of both legacy control and
   NET to NIC control.  The capability negotiation between NICs and
   Switches can be considered either some in-band ECN-like negotiations
   or out-of-band individual message negotiations.

6.2.  Co-exist with current NIC to NIC control channel

   In this architecture, NET to NIC control channel can co-exist with
   NIC to NIC control channel.  It can be an additional control channel
   for better congestion control.

   Once the NET-to-NIC channel of a sender is enabled on a switch, it
   will signal the congestion information back to the sender through
   this channel.  While for hosts without NET control, the switch works
   the same as the legacy switches when congestion happens.

   For receivers that detect the congestion based on lost packets,
   packets marked CE due to congestion on legacy network nodes, or the
   exhaustion of local resources, they can still notify the senders
   according to the congestion control algorithms.  The senders evaluate
   the messages based on its local polices, e.g., if it receives a
   message from the net-control interface prior to the message from the
   receiver in certain period, it may decide to make decision based on
   the net-control message; While if there's no net-control message
   received, the sender may react according to the message from the
   receiver.

   Please note that NET to NIC control channel SHOULD be implemented as
   an option rather than a mandatory feature.

7.  Security Considerations

   TBD








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8.  Manageability Consideration

   TBD

9.  IANA Considerations

   No IANA action

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2.  Informative References

   [HotCocoa]
              Arashloo, M. T., Ghobadi, M., Rexford, J., and D. Walker,
              "HotCocoa: Hardward Congestion Control Abstractions", 11
              2017, <https://www.cs.princeton.edu/~jrex/papers/
              hotcocoa17.pdf>.

   [HPC]      Cardona, O., "Towards Hyperscale High Performance
              Computing with RDMA", 6 2019,
              <https://pc.nanog.org/static/published/meetings/NANOG76/19
              99/20190612_Cardona_Towards_Hyperscale_High_v1.pdf>.

   [IB]       "Infiniband Trade Association.  InfiniBandTM Architecture
              Specification Volume 1 and Volume 2.",
              <https://cw.infinibandta.org/document/dl/7781>.

   [Requirement]
              Chen, F., Sun, W., Yu, X., and R. Even, "Data Center
              Congestion Management requirements", 6 2019,
              <https://datatracker.ietf.org/doc/html/
              draft-yueven-tsvwg-dccm-requirements>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <https://www.rfc-editor.org/info/rfc3168>.



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   [RFC5040]  Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
              Garcia, "A Remote Direct Memory Access Protocol
              Specification", RFC 5040, DOI 10.17487/RFC5040, October
              2007, <https://www.rfc-editor.org/info/rfc5040>.

Authors' Addresses

   Yan Zhuang
   Huawei Technologies Co., Ltd.

   Email: zhuangyan.zhuang@huawei.com


   Rachel Huang
   Huawei Technologies Co., Ltd.

   Email: rachel.huang@huawei.com


































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