[PATCH v3 0/1] introduce virtio-ism: internal shared memory device

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

Hello everyone,

# Background

    Nowadays, there is a common scenario to accelerate communication between
    different VMs and containers, including light weight virtual machine based
    containers. One way to achieve this is to colocate them on the same host.
    However, the performance of inter-VM communication through network stack is
    not optimal and may also waste extra CPU cycles. This scenario has been
    discussed many times, but still no generic solution available [1] [2] [3].

    With pci-ivshmem + SMC(Shared Memory Communications: [4]) based PoC[5],
    We found that by changing the communication channel between VMs from TCP to
    SMC with shared memory, we can achieve superior performance for a common
    socket-based application[5]:
      - latency reduced by about 50%
      - throughput increased by about 300%
      - CPU consumption reduced by about 50%

    Since there is no particularly suitable shared memory management solution
    matches the need for SMC(See ## Comparison with existing technology), and
    virtio is the standard for communication in the virtualization world, we
    want to implement a virtio-ism device based on virtio, which can support
    on-demand memory sharing across VMs, containers or VM-container. To match
    the needs of SMC, the virtio-ism device need to support:

    1. Dynamic provision: shared memory regions are dynamically allocated and
       provisioned.
    2. Multi-region management: the shared memory is divided into regions,
       and a peer may allocate one or more regions from the same shared memory
       device.
    3. Permission control: the permission of each region can be set seperately.
    4. Dynamic connection: each ism region of a device can be shared with
       different devices, eventually a device can be shared with thousands of
       devices

# Virtio ISM device

    An ISM(Internal Shared Memory) device provides the ability to access memory
    shared between multiple devices. This allows low-overhead communication in
    presence of such memory. For example, memory can be shared with guests of
    multiple virtual machines running on the same host, with each virtual
    machine including an ism device and with the guests getting the shared
    memory by the ism devices.

    An ism device can communicate with multiple peers simultaneously. This
    communication can be dynamically started and ended.

## Design

    This is a structure diagram based on ism sharing between two vms.

    |-------------------------------------------------------------------------------------------------------------|
    | |------------------------------------------------|       |------------------------------------------------| |
    | | Guest                                          |       | Guest                                          | |
    | |                                                |       |                                                | |
    | |   ----------------                             |       |   ----------------                             | |
    | |   |    driver    |     [M1]   [M2]   [M3]      |       |   |    driver    |             [M2]   [M3]     | |
    | |   ----------------       |      |      |       |       |   ----------------               |      |      | |
    | |    |cq|                  |map   |map   |map    |       |    |cq|                          |map   |map   | |
    | |    |  |                  |      |      |       |       |    |  |                          |      |      | |
    | |    |  |                -------------------     |       |    |  |                --------------------    | |
    | |----|--|----------------|  device memory  |-----|       |----|--|----------------|  device memory   |----| |
    | |    |  |                -------------------     |       |    |  |                --------------------    | |
    | |                                |               |       |                               |                | |
    | |                                |               |       |                               |                | |
    | | Qemu                           |               |       | Qemu                          |                | |
    | |--------------------------------+---------------|       |-------------------------------+----------------| |
    |                                  |                                                       |                  |
    |                                  |                                                       |                  |
    |                                  |------------------------------+------------------------|                  |
    |                                                                 |                                           |
    |                                                                 |                                           |
    |                                                   --------------------------                                |
    |                                                    | M1 |   | M2 |   | M3 |                                 |
    |                                                   --------------------------                                |
    |                                                                                                             |
    | HOST                                                                                                        |
    ---------------------------------------------------------------------------------------------------------------

## Inspiration

    Our design idea for virtio-ism comes from IBM's ISM device, to pay tribute,
    we directly name this device "ism".

    Information about IBM ism device and SMC:
      1. SMC reference: https://www.ibm.com/docs/en/zos/2.5.0?topic=system-shared-memory-communications
      2. SMC-Dv2 and ISMv2 introduction: https://www.newera.com/INFO/SMCv2_Introduction_10-15-2020.pdf
      3. ISM device: https://www.ibm.com/docs/en/linux-on-systems?topic=n-ism-device-driver-1
      4. SMC protocol (including SMC-D): https://www.ibm.com/support/pages/system/files/inline-files/IBM%20Shared%20Memory%20Communications%20Version%202_2.pdf
      5. SMC-D FAQ: https://www.ibm.com/support/pages/system/files/inline-files/2021-02-09-SMC-D-FAQ.pdf

## ISM VLAN

    Since SMC uses TCP to handshake with IP facilities, virtio-ism device is not
    bound to existing IP device, and the latest ISMv2 device doesn't require
    VLAN. So it is not necessary for virtio-ism to support VLAN attributes.

## Live Migration

    Currently SMC-D doesn't support migration to another device or fallback. And
    SMC-R supports migration to another link, no fallback.

    So we may not support live migration for the time being.

## About hot plugging of the ism device

    Hot plugging of devices is a heavier, possibly failed, time-consuming, and
    less scalable operation. So, we don't plan to support it for now.


# Usage (SMC as example)

    There is one of possible use cases:

    1. SMC calls the interface ism_alloc_region() of the ism driver to return
       the location of a memory region in the PCI space and a token.
    2. The ism driver mmap the memory region and return to SMC with the token
    3. SMC passes the token to the connected peer
    4. the peer calls the ism driver interface ism_attach_region(token) to
       get the location of the PCI space of the shared memory
    5. The connected pair communicating through the shared memory

# Comparison with existing technology

## ivshmem or ivshmem 2.0 of Qemu

   1. ivshmem 1.0 is a large piece of memory that can be seen by all devices
      that use this VM, so the security is not enough.

   2. ivshmem 2.0 is a shared memory belonging to a VM that can be read-only by
      all other VMs that use the ivshmem 2.0 shared memory device, which also
      does not meet our needs in terms of security.

## vhost-pci and virtiovhostuser

    1. does not support dynamic allocation
    2. one device just support connect to one vm


# POC CODE

There are no functions related to eventq and perm yet.
This implementation is for V2 version spec.

## Qemu (virtio ism device):

     https://github.com/fengidri/qemu/compare/7d66b74c4dd0d74d12c1d3d6de366242b13ed76d...ism-upstream-1216?expand=1

    Start qemu with option "--device virtio-ism-pci,disable-legacy=on, disable-modern=off".

##  Kernel (virtio ism driver and smc support):

     https://github.com/fengidri/linux-kernel-virtio-ism/compare/6f8101eb21bab480537027e62c4b17021fb7ea5d...ism-upstream-1223


### SMC

    Support SMC-D works with virtio-ism.

    Use SMC with virtio-ism to accelerate inter-VM communication.

    1. insmod virtio-ism and smc module.
    2. use smc-tools [1] to get the device name of SMC-D based on virtio-ism.

      $ smcd d # here is _virtio2_
      FID  Type  PCI-ID        PCHID  InUse  #LGs  PNET-ID
      0000 0     virtio2       0000   Yes       1  *C1

    3. add the nic and SMC-D device to the same pnet, do it in both client and server.

      $ smc_pnet -a -I eth1 c1 # use eth1 to setup SMC connection
      $ smc_pnet -a -D virtio2 c1 # virtio2 is the virtio-ism device

    4. use SMC to accelerate your application, smc_run in [1] can do this.

      # smc_run use LD_PRELOAD to hijack socket syscall with AF_SMC
      $ smc_run sockperf server --tcp # run in server
      $ smc_run sockperf tp --tcp -i a.b.c.d # run in client

    [1] https://github.com/ibm-s390-linux/smc-tools

    Notice: The current POC state, we only tested some basic functions.

### App inside user space

    The ism driver provide /dev/vismX interface, allow users to use Virtio-ISM
    device in user space directly.

    Try tools/virtio/virtio-ism/virtio-ism-mmap

    Usage:
         cd tools/virtio/virtio-ism/; make
         insmode virtio-ism.ko

    case1: communicate

       vm1: ./virtio-ism-mmap alloc -> token
       vm2: ./virtio-ism-mmap attach -t <token> --write-msg AAAA --commit

       vm2 will write msg to shared memory, then notify vm1. After vm1 receive
       notify, then read from shared memory.

    case2: ping-pong test.

        vm1: ./virtio-ism-mmap server
        vm2: ./virtio-ism-mmap -i 192.168.122.101 pp

        1. server alloc one ism region
        2. client get the token by tcp

        3. client commit(kick) to server, server recv notify, commit(kick) to client
        4. loop #3

    case3: throughput test.

        vm1: ./virtio-ism-mmap server
        vm2: ./virtio-ism-mmap -i 192.168.122.101 tp

        1. server alloc one ism region
        2. client get the token by tcp

        3. client write 1M data to ism region
        4. client commit(kick) to server
        5. server recv notify, copy the data, the commit(kick) back to client
        6. loop #3-#5

    case4: throughput test with protocol defined by user.

        vm1: ./virtio-ism-mmap server
        vm2: ./virtio-ism-mmap -i 192.168.122.101 tp --polling --tp-chunks 15 --msg-size 64k -n 50000

        Used the ism region as a ring.

        In this scene, client and server are in the polling mode. Test it on
        my machine, the maximum can reach 12GBps

# References

    [1] https://projectacrn.github.io/latest/tutorials/enable_ivshmem.html
    [2] https://dl.acm.org/doi/10.1145/2847562
    [3] https://hal.archives-ouvertes.fr/hal-00368622/document
    [4] https://lwn.net/Articles/711071/
    [5] https://lore.kernel.org/netdev/20220720170048.20806-1-tonylu@linux.alibaba.com/T/


If there are any problems, please point them out.
Hope to hear from you, thank you.

v3:
   1. support to apply memory from vm
   2. add query operation
   3. optimize the description of spec and enrich some details
   4. use the communication domain as a term
   5. replace gid with cdid

v2:
   1. add Attach/Detach event
   2. add Events Filter
   3. allow Alloc/Attach huge region
   4. remove host/guest terms

v1:
   1. cover letter adding explanation of ism vlan
   2. spec add gid
   3. explain the source of ideas about ism
   4. POC support virtio-ism-smc.ko virtio-ism-dev.ko and support virtio-ism-mmap


Xuan Zhuo (1):
  virtio-ism: introduce new device virtio-ism

 conformance.tex |  26 +++
 content.tex     |   1 +
 virtio-ism.tex  | 573 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 600 insertions(+)
 create mode 100644 virtio-ism.tex

-- 
2.32.0.3.g01195cf9f