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Subject: [PATCH v1 0/2] introduce virtio-ism: internal shared memory device
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
ISM devices provide the ability to share memory between different guests on
a host. A guest's memory got from ism device can be shared with multiple
peers at the same time. This shared relationship can be dynamically created
and released.
The shared memory obtained from the device is divided into multiple ism
regions for share. ISM device provides a mechanism to notify other ism
region referrers of content update events.
## 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
## Qemu:
https://github.com/fengidri/qemu/compare/7422cd20c4780ccdc7395d2dfaee33cb7d246d43...ism?expand=1
Start qemu with option "--device virtio-ism-pci,disable-legacy=on, disable-modern=off".
## Kernel (ism driver and smc support):
https://github.com/fengidri/linux-kernel-virtio-ism/compare/6f8101eb21bab480537027e62c4b17021fb7ea5d...xuanzhuo/smc-d-virtio-ism
There are three modules:
virtio-ism.ko
virtio-ism-smc.ko
virtio-ism-dev.ko.
The latter two modules depend on the first one.
virtio-ism-smc.ko virtio-ism-dev.ko should not be used at the same time.
### virtio-ism-smc.ko
Support SMC-D works with virtio-ism.
Use SMC with virtio-ism to accelerate inter-VM communication.
1. insmod virtio-ism-smc module, this module bridges SMC and virio-ism.
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.
### virtio-ism-dev.ko
Provide /dev/virtio-ism interface, allow users to use Virtio-ISM device
directly.
Try tools/virtio/virtio-ism/virtio-ism-mmap.c
Usage:
insmod virtio-ism-dev module.
vm1: virtio-ism-mmap alloc -> token
vm2: virtio-ism-mmap attach <token>
vm1 will write to shared memory, then notify vm2.
After vm2 receive notify, then read from shared memory.
# 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.
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 (2):
Reserve device id for ISM device
virtio-ism: introduce new device virtio-ism
content.tex | 3 +
virtio-ism.tex | 350 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 353 insertions(+)
create mode 100644 virtio-ism.tex
--
2.32.0.3.g01195cf9f
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