Re: [RFC PATCH net-next v4 0/9] net/smc: Introduce SMC-D-based OS internal communication acceleration

Wenjia Zhang
2023-04-05T14:48:32Z

On 27.03.23 05:28, Wen Gu wrote:
> Hi, all
>
> # Background
>
> The background and previous discussion can be referred from [1],[6].
>
> 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, 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 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. :)
>
> 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 needs that the loopback device GID is globally unique. But theoretically
> there is a possibility of a collision. Assume the following situations:
>
> (1) Assume that the SMC-D loopback devices of the two different 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) And 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.
> But 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 is acceptable? Can we just use 64-bits random generated number as GID in
> loopback device?
>
> Some other ways that may be able to make loopback GID unique are
> 1) 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 needs
> to extend the CLC message to carry a longer GID.
> 2) Using MAC address of netdev in the OS as part of SMC-D loopback device GID, provided
> that the MAC addresses are unique. But the MAC address could theoretically also be
> incorrectly set to be the same.
>
> Hope to hear opinions from the community. Any ideas are welcome.
>
> Thanks!
> Wen Gu

Hi Wen,

Thank you for the new version. The discussion on the open issue is still
on-going in our organisation internally. I appreciate your patience!

One thing I need to mention during testing the loopback device on our
platform is that we get crash, because smc_ism-signal_shutdown() is
called by smc_1gr_free_work(), which is called indirectly by
smc_conn_free(). Please make sure that it would go to the path of the
loopback device cleanly. Any question and consideration is welcome!

Thanks,
Wenjia
>
> v4->v3
> 1. Rebase to the latest net-next;
> 2. Introduce SEID helper. SMC-D loopback will return SMCD_DEFAULT_V2_SEID. And if it
> coexist with ISM device, the SEID of ISM device will overwrite SMCD_DEFAULT_V2_SEID
> as smc_ism_v2_system_eid.
> 3. Won't remove dmb_node from hashtable until no sndbuf attaching to it.
>
> Something postponed in this version
> 1. Hierarchy perference of SMC-D devices when loopback and ISM devices coexist, which
> will be determinated after comparing the performance of loopback and ISM.
>
> 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/
> [6] https://lore.kernel.org/netdev/1676477905-88043-1-git-send-email-guwen@linux.alibaba.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 | 99 ++++++++--
> net/smc/smc_ism.h | 5 +
> net/smc/smc_loopback.c | 445 +++++++++++++++++++++++++++++++++++++++++++++
> net/smc/smc_loopback.h | 56 ++++++
> 12 files changed, 750 insertions(+), 37 deletions(-)
> create mode 100644 net/smc/smc_loopback.c
> create mode 100644 net/smc/smc_loopback.h
>