From: Ursula Braun <ursula.braun@xxxxxxxxxx>
In 2013, IBM introduced an optimized communications solution for the
IBM zEnterprise EC12 and BC12 (s390 in Linux terminology) that is
comprised of the IBM 10GbE RoCE Express feature with Shared Memory
Communications-RDMA (SMC-R) protocol [1].
SMC-R is designed for the enterprise data center environment and is an open
protocol as specified in the informational RFC [2]. The final draft
submitted by IBM has been approved for publication and is in the final
editorial stage. Another implementation of this protocol is available since
2013 with IBM z/OS Version 2 Release 1.
SMC-R provides a “sockets over RDMA” solution that leverages industry
standard RDMA over Converged Ethernet (RoCE) technology.
IBM has developed a Linux implementation of the SMC-R standard. A new
socket protocol family AF_SMC is introduced. A preload library can be used
to enable TCP-based applications to use SMC-R without changes.
Key aspects of SMC-R are:
1. Provides optimized performance compared to standard TCP/IP over Ethernet
within the data center for both request/response (latency) and streaming
workloads (CPU savings) [3].
Initial benchmarks on Linux on x86 processors have shown latency
reduction of up to 52% with a throughput gain of 111% using SMC-R vs TCP
for request/response message patterns (10 concurrent TCP connections
with 16KB messages) and CPU savings of up to 69% for streaming data
patterns (single TCP connection with 20MB of data in one direction).
[1] is currently updated to contain more detailed information on Linux
and performance.
2. In order to preserve the traditional network administrative model the
SMC-R protocol ties into the existing IP addresses and uses TCP's
handshake to establish connections. This allows existing management
tools and security infrastructure to control the creation of SMC
connections.
3. The SMC-R protocol logically bonds multiple RoCE adapters together
providing redundancy with transparent fail-over for improved high
availability, increased bandwidth and load balancing across multiple
RDMA-capable devices.
4. Due to its handshake protocol, SMC-R is compatible with (transparent to)
existing TCP connection load balancers that are commonly used in the
enterprise data center environment for multi-tier application workloads.
5. SMC-R's handshake protocol allows for transparent fallback to TCP/IP,
should one of the peers not be capable of the protocol.
Additional SMC-R overview and reference materials are available [1].
The SMC-R “rendezvous" protocol eliminates the need for RDMA-CM and the
exchange occurs through an initial TCP connection. Building on a TCP
connection to establish an SMC-R connection solves many key requirements,
including #4 and #5 above.
The rendezvous process occurs in 2 phases:
1. TCP/IP 3-way exchange:
Initiated when both client and server indicate SMC-R capability by
including TCP experimental options on the TCP/IP 3-way handshake (syn
flows) as described in RFC6994 [4]. The ExID assigned by IANA is
0xE2D4C3D9 [5].
2. SMC-R 3-way exchange:
When both partners indicate SMC-R capability then at the completion of
the 3-way TCP handshake the SMC-R layers in each peer take control of
the TCP connection and exchange their RDMA credentials. If this 3-way
exchange completes successfully the connection continues using SMC-R.
If the exchange is not successful the connections falls back to standard
TCP/IP.
References:
[1] SMC-R Overview and Reference Materials:
http://www-01.ibm.com/software/network/commserver/SMCR/
[2] SMC-R Informational RFC:
http://tools.ietf.org/html/draft-fox-tcpm-shared-memory-rdma-07
[3] Linux SMC-R Overview and Performance Summary
(archs x86 and s390):
http://www-01.ibm.com/software/network/commserver/SMCR/
[4] Shared Use of TCP Experimental Options RFC 6994:
https://tools.ietf.org/rfc/rfc6994.txt
[5] IANA ExID SMCR:
http://www.iana.org/assignments/tcp-parameters/tcp-parameters.xhtml#tcp-exids
The patch series is prepared to apply to net-next and consists of these
parts:
1. net/ipv4/tcp: TCP experimental option
2. net: definitions to establish new socket family
3. net/smc: new socket family
In the future, SMC-R will be enhanced to cover:
- IPv6 support
- Tracing
- Statistics support
Thanks,
Ursula
Ursula Braun (3):
tcp: introduce TCP experimental option for SMC
net: introduce socket family constants
smc: introduce socket family AF_SMC
include/linux/socket.h | 4 +-
include/linux/tcp.h | 5 +-
include/net/request_sock.h | 3 +-
include/net/smc.h | 13 +
include/net/tcp.h | 3 +
net/Kconfig | 1 +
net/Makefile | 1 +
net/ipv4/tcp_input.c | 12 +
net/ipv4/tcp_minisocks.c | 4 +
net/ipv4/tcp_output.c | 28 +
net/smc/Kconfig | 9 +
net/smc/Makefile | 3 +
net/smc/af_smc.c | 3142 ++++++++++++++++++++++++++++++++++++++++++
net/smc/af_smc.h | 689 ++++++++++
net/smc/smc_core.c | 3291 ++++++++++++++++++++++++++++++++++++++++++++
net/smc/smc_llc.c | 1597 +++++++++++++++++++++
net/smc/smc_llc.h | 192 +++
net/smc/smc_proc.c | 884 ++++++++++++
18 files changed, 9878 insertions(+), 3 deletions(-)
create mode 100644 include/net/smc.h
create mode 100644 net/smc/Kconfig
create mode 100644 net/smc/Makefile
create mode 100644 net/smc/af_smc.c
create mode 100644 net/smc/af_smc.h
create mode 100644 net/smc/smc_core.c
create mode 100644 net/smc/smc_llc.c
create mode 100644 net/smc/smc_llc.h
create mode 100644 net/smc/smc_proc.c
--
2.3.8
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