Re: [RFC PATCH net-next v3 0/9] net/smc: Introduce SMC-D-based OS internal communication acceleration

Wenjia Zhang
2023-02-22T13:08:29Z

On 22.02.23 13:00, Wen Gu wrote:
>
>
> On 2023/2/16 00:18, Wen Gu wrote:
>
>> Hi, all
>>
>> # Background
>>
>> The background and previous discussion can be referred from [1].
>>
>> We found SMC-D can be used to accelerate OS internal communication,
>> such as
>> loopback or between two containers within the same OS instance. So
>> this patch
>> set provides a kind of SMC-D dummy device (we call it the SMC-D
>> loopback device)
>> to emulate an ISM device, so that SMC-D can also be used on architectures
>> other than s390. The SMC-D loopback device are designed as a system
>> global
>> device, visible to all containers.
>>
>> This version is implemented based on the generalized interface
>> provided by [2].
>> And there is an open issue of this version, which will be mentioned
>> later.
>>
>> # Design
>>
>> This patch set basically follows the design of the previous version.
>>
>> Patch #1/9 ~ #3/9 attempt to decouple ISM-related structures from the
>> SMC-D
>> generalized code and extract some helpers to make SMC-D protocol
>> compatible
>> with devices other than s390 ISM device.
>>
>> Patch #4/9 introduces a kind of loopback device, which is defined as
>> SMC-D v2
>> device and designed to provide communication between SMC sockets in
>> the same OS
>> instance.
>>
>>   +-------------------------------------------+
>>   |  +--------------+       +--------------+  |
>>   |  | SMC socket A |       | SMC socket B |  |
>>   |  +--------------+       +--------------+  |
>>   |       ^                         ^         |
>>   |       |    +----------------+   |         |
>>   |       |    |   SMC stack    |   |         |
>>   |       +--->| +------------+ |<--|         |
>>   |            | |   dummy    | |             |
>>   |            | |   device   | |             |
>>   |            +-+------------+-+             |
>>   |                   OS                      |
>>   +-------------------------------------------+
>>
>> Patch #5/9 ~ #8/9 expand SMC-D protocol interface (smcd_ops) for
>> scenarios where
>> SMC-D is used to communicate within VM (loopback here) or between VMs
>> on the same
>> host (based on virtio-ism device, see [3]). What these scenarios have
>> in common
>> is that the local sndbuf and peer RMB can be mapped to same physical
>> memory region,
>> so the data copy between the local sndbuf and peer RMB can be omitted.
>> Performance
>> improvement brought by this extension can be found in # Benchmark Test.
>>
>>   +----------+                     +----------+
>>   | socket A |                     | socket B |
>>   +----------+                     +----------+
>>         |                               ^
>>         |         +---------+           |
>>    regard as      |         | ----------|
>>    local sndbuf   |  B's    |     regard as
>>         |         |  RMB    |     local RMB
>>         |-------> |         |
>>                   +---------+
>>
>> Patch #9/9 realizes the support of loopback device for the
>> above-mentioned expanded
>> SMC-D protocol interface.
>>
>> # Benchmark Test
>>
>>   * Test environments:
>>        - VM with Intel Xeon Platinum 8 core 2.50GHz, 16 GiB mem.
>>        - SMC sndbuf/RMB size 1MB.
>>
>>   * Test object:
>>        - TCP lo: run on TCP loopback.
>>        - domain: run on UNIX domain.
>>        - SMC lo: run on SMC loopback device with patch #1/9 ~ #4/9.
>>        - SMC lo-nocpy: run on SMC loopback device with patch #1/9 ~ #9/9.
>>
>> 1. ipc-benchmark (see [4])
>>
>>   - ./<foo> -c 1000000 -s 100
>>
>>                      TCP-lo              domain
>> SMC-lo          SMC-lo-nocpy
>> Message
>> rate (msg/s)         79025      115736(+46.45%)
>> 146760(+85.71%)       149800(+89.56%)
>>
>> 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-lo                  SMC-lo
>> SMC-lo-nocpy
>> Bandwidth(MBps)   4822.388        4940.918(+2.56%)
>> 8086.67(+67.69%)
>> Latency(us)          6.298          3.352(-46.78%)
>> 3.35(-46.81%)
>>
>> 3. iperf3
>>
>>   - serv: <smc_run> taskset -c <cpu> iperf3 -s
>>   - clnt: <smc_run> taskset -c <cpu> iperf3 -c 127.0.0.1 -t 15
>>
>>                      TCP-lo                  SMC-lo
>> SMC-lo-nocpy
>> Bitrate(Gb/s)         40.7            40.5(-0.49%)
>> 72.4(+77.89%)
>>
>> 4. nginx/wrk
>>
>>   - serv: <smc_run> nginx
>>   - clnt: <smc_run> wrk -t 8 -c 500 -d 30 http://127.0.0.1:80
>>
>>                      TCP-lo                  SMC-lo
>> SMC-lo-nocpy
>> Requests/s       155994.57      214544.79(+37.53%)
>> 215538.55(+38.17%)
>>
>>
>> # Open issue
>>
>> The open issue has not been resolved now is about how to detect that
>> the source
>> and target of CLC proposal are within the same OS instance and can
>> communicate
>> through the SMC-D loopback device. Similar issue also exists when
>> using virtio-ism
>> devices (the background and details of virtio-ism device can be
>> referred from [3]).
>> In previous discussions, multiple options were proposed (see [5]).
>> Thanks again for
>> the help of the community. cc Alexandra Winter :)
>>
>> But as we discussed, these solutions have some imperfection. So this
>> version of RFC
>> continues to use previous workaround, that is, a 64-bit random GID is
>> generated for
>> SMC-D loopback device. If the GIDs of the devices found by two peers
>> are the same,
>> then they are considered to be in the same OS instance and can
>> communicate with each
>> other by the loopback device.
>>
>> This approach has very small risk. Assume the following situations:
>>
>> (1) Assume that the SMC-D loopback devices of the two OS instances
>> happen to
>>      generate the same 64-bit GID.
>>
>>      For the convenience of description, we refer to the sockets on
>> these two
>>      different OS instance as server A and client B.
>>
>>      A will misjudge that the two are on the same OS instance because
>> the same GID
>>      in CLC proposal message. Then A creates its RMB and sends 64-bit
>> token-A to B
>>      in CLC accept message.
>>
>>      B receives the CLC accept message. And according to patch #7/9, B
>> tries to
>>      attach its sndbuf to A's RMB by token-A.
>>
>> (2) Assume that the OS instance where B is located happens to have an
>> unattached
>>      RMB whose 64-bit token is same as token-A.
>>
>>      Then B successfully attaches its sndbuf to the wrong RMB, and
>> creates its RMB,
>>      sends token-B to A in CLC confirm message.
>>
>>      Similarly, A receives the message and tries to attach its sndbuf
>> to B's RMB by
>>      token-B.
>>
>> (3) Similar to (2), assume that the OS instance where A is located
>> happens to have
>>      an unattached RMB whose 64-bit token is same as token-B.
>>
>>      Then A successfully attach its sndbuf to the wrong RMB. Both
>> sides mistakenly
>>      believe that an SMC-D connection based on the loopback device is
>> established
>>      between them.
>>
>> If the above 3 coincidences all happen, that is, 64-bit random number
>> conflicts occur
>> 3 times, then an unreachable SMC-D connection will be established,
>> which is nasty.
>> If one of above is not satisfied, it will safely fallback to TCP.
>>
>> Since the chances of these happening are very small, I wonder if this
>> risk of 1/2^(64*3)
>> probability can be tolerated ?
>
> Hi,
>
> Any comments about this open issue or other parts of this RFC patch set? :)
>
> Thanks,
> Wen Gu
>
Hi Wen,

I don't forget it ;) I'm trying to run it by myself. Please give us more
time for the trying and review.

Thanks
Wenjia

>> Another way to solve this open issue is using a 128-bit UUID to
>> identify SMC-D loopback
>> device or virtio-ism device, because the probability of a 128-bit UUID
>> collision is
>> considered negligible. But it may need to extend the CLC message to
>> carry a longer GID,
>> which is the last option.
>>
>> v3->v2
>>   1. Adapt new generalized interface provided by [2];
>>   2. Select loopback device through SMC-D v2 protocol;
>>   3. Split the loopback-related implementation and generic
>> implementation into different
>>      patches more reasonably.
>>
>> v1->v2
>>   1. Fix some build WARNINGs complained by kernel test rebot
>>      Reported-by: kernel test robot <lkp@intel.com>
>>   2. Add iperf3 test data.
>>
>> [1]
>> https://lore.kernel.org/netdev/1671506505-104676-1-git-send-email-guwen@linux.alibaba.com/
>> [2]
>> https://lore.kernel.org/netdev/20230123181752.1068-1-jaka@linux.ibm.com/
>> [3]
>> https://lists.oasis-open.org/archives/virtio-comment/202302/msg00148.html
>> [4] https://github.com/goldsborough/ipc-bench
>> [5]
>> https://lore.kernel.org/netdev/b9867c7d-bb2b-16fc-feda-b79579aa833d@linux.ibm.com/
>>
>> Wen Gu (9):
>>    net/smc: Decouple ism_dev from SMC-D device dump
>>    net/smc: Decouple ism_dev from SMC-D DMB registration
>>    net/smc: Extract v2 check helper from SMC-D device registration
>>    net/smc: Introduce SMC-D loopback device
>>    net/smc: Introduce an interface for getting DMB attribute
>>    net/smc: Introudce interfaces for DMB attach and detach
>>    net/smc: Avoid data copy from sndbuf to peer RMB in SMC-D
>>    net/smc: Modify cursor update logic when using mappable DMB
>>    net/smc: Add interface implementation of loopback device
>>
>>   drivers/s390/net/ism_drv.c |   5 +-
>>   include/net/smc.h          |  18 +-
>>   net/smc/Makefile           |   2 +-
>>   net/smc/af_smc.c           |  26 ++-
>>   net/smc/smc_cdc.c          |  59 ++++--
>>   net/smc/smc_cdc.h          |   1 +
>>   net/smc/smc_core.c         |  70 ++++++-
>>   net/smc/smc_core.h         |   1 +
>>   net/smc/smc_ism.c          |  79 ++++++--
>>   net/smc/smc_ism.h          |   4 +
>>   net/smc/smc_loopback.c     | 442
>> +++++++++++++++++++++++++++++++++++++++++++++
>>   net/smc/smc_loopback.h     |  55 ++++++
>>   12 files changed, 725 insertions(+), 37 deletions(-)
>>   create mode 100644 net/smc/smc_loopback.c
>>   create mode 100644 net/smc/smc_loopback.h
>>