[RFC,net-next,0/5] Introduce SMC-D based loopback acceleration

  Hi, all

# Background

As previously mentioned in [1], we (Alibaba Cloud) are trying to use SMC
to accelerate TCP applications in cloud environment, improving inter-host
or inter-VM communication.

In addition of these, we also found the value of SMC-D in scenario of local
inter-process communication, such as accelerate communication between containers
within the same host. So this RFC tries to provide a SMC-D loopback solution
in such scenario, to bring a significant improvement in latency and throughput
compared to TCP loopback.

# Design

This patch set provides a kind of SMC-D loopback solution.

Patch #1/5 and #2/5 provide an SMC-D based dummy device, preparing for the
inter-process communication acceleration. Except for loopback acceleration,
the dummy device can also meet the requirements mentioned in [2], which is
providing a way to test SMC-D logic for broad community without ISM device.

 +------------------------------------------+
 |  +-----------+           +-----------+   |
 |  | process A |           | process B |   |
 |  +-----------+           +-----------+   |
 |       ^                        ^         |
 |       |    +---------------+   |         |
 |       |    |   SMC stack   |   |         |
 |       +--->| +-----------+ |<--|         |
 |            | |   dummy   | |             |
 |            | |   device  | |             |
 |            +-+-----------+-+             |
 |                   VM                     |
 +------------------------------------------+

Patch #3/5, #4/5, #5/5 provides a way to avoid data copy from sndbuf to RMB
and improve SMC-D loopback performance. Through extending smcd_ops with two
new semantic: attach_dmb and detach_dmb, sender's sndbuf shares the same
physical memory region with receiver's RMB. The data copied from userspace
to sender's sndbuf directly reaches the receiver's RMB without unnecessary
memory copy in the same kernel.

 +----------+                     +----------+
 | socket A |                     | socket B |
 +----------+                     +----------+
       |                               ^
       |         +---------+           |
  regard as      |         | ----------|
  local sndbuf   |  B's    |     regard as
       |         |  RMB    |     local RMB
       |-------> |         |
                 +---------+

# Benchmark Test

 * Test environments:
      - VM with Intel Xeon Platinum 8 core 2.50GHz, 16 GiB mem.
      - SMC sndbuf/RMB size 1MB.

 * Test object:
      - TCP: run on TCP loopback.
      - domain: run on UNIX domain.
      - SMC lo: run on SMC loopback device with patch #1/5 ~ #2/5.
      - SMC lo-nocpy: run on SMC loopback device with patch #1/5 ~ #5/5.

1. ipc-benchmark (see [3])

 - ./<foo> -c 1000000 -s 100

                       TCP              domain              SMC-lo             SMC-lo-nocpy
Message
rate (msg/s)         75140      129548(+72.41)    152266(+102.64%)         151914(+102.17%)

2. sockperf

 - serv: <smc_run> taskset -c <cpu> sockperf sr --tcp
 - clnt: <smc_run> taskset -c <cpu> sockperf { tp | pp } --tcp --msg-size={ 64000 for tp | 14 for pp } -i 127.0.0.1 -t 30

                       TCP                  SMC-lo             SMC-lo-nocpy
Bandwidth(MBps)   4943.359        4936.096(-0.15%)        8239.624(+66.68%)
Latency(us)          6.372          3.359(-47.28%)            3.25(-49.00%)

3. nginx/wrk

 - serv: <smc_run> nginx
 - clnt: <smc_run> wrk -t 8 -c 500 -d 30 http://127.0.0.1:80

                       TCP                   SMC-lo             SMC-lo-nocpy
Requests/s       154643.22       220894.03(+42.84%)        226754.3(+46.63%)


# Discussion

1. API between SMC-D and ISM device

As Jan mentioned in [2], IBM are working on placing an API between SMC-D
and the ISM device for easier use of different "devices" for SMC-D.

So, considering that the introduction of attach_dmb or detach_dmb can
effectively avoid data copying from sndbuf to RMB and brings obvious
throughput advantages in inter-VM or inter-process scenarios, can the
attach/detach semantics be taken into consideration when designing the
API to make it a standard ISM device behavior?

Maybe our RFC of SMC-D based inter-process acceleration (this one) and
inter-VM acceleration (will coming soon, which is the update of [1])
can provide some examples for new API design. And we are very glad to
discuss this on the mail list.

2. Way to select different ISM-like devices

With the proposal of SMC-D loopback 'device' (this RFC) and incoming
device used for inter-VM acceleration as update of [1], SMC-D has more
options to choose from. So we need to consider that how to indicate
supported devices, how to determine which one to use, and their priority...

IMHO, this may require an update of CLC message and negotiation mechanism.
Again, we are very glad to discuss this with you on the mailing list.

[1] https://lore.kernel.org/netdev/20220720170048.20806-1-tonylu@linux.alibaba.com/
[2] https://lore.kernel.org/netdev/35d14144-28f7-6129-d6d3-ba16dae7a646@linux.ibm.com/
[3] https://github.com/goldsborough/ipc-bench


Wen Gu (5):
  net/smc: introduce SMC-D loopback device
  net/smc: choose loopback device in SMC-D communication
  net/smc: add dmb attach and detach interface
  net/smc: avoid data copy from sndbuf to peer RMB in SMC-D loopback
  net/smc: logic of cursors update in SMC-D loopback connections

 include/net/smc.h      |   3 +
 net/smc/Makefile       |   2 +-
 net/smc/af_smc.c       |  88 +++++++++++-
 net/smc/smc_cdc.c      |  59 ++++++--
 net/smc/smc_cdc.h      |   1 +
 net/smc/smc_clc.c      |   4 +-
 net/smc/smc_core.c     |  62 +++++++++
 net/smc/smc_core.h     |   2 +
 net/smc/smc_ism.c      |  39 +++++-
 net/smc/smc_ism.h      |   2 +
 net/smc/smc_loopback.c | 365 +++++++++++++++++++++++++++++++++++++++++++++++++
 net/smc/smc_loopback.h |  63 +++++++++
 12 files changed, 669 insertions(+), 21 deletions(-)
 create mode 100644 net/smc/smc_loopback.c
 create mode 100644 net/smc/smc_loopback.h