NVMe Computational Storage Devices based on Open-Source Software and readily available Hardware

This project aims to allow anyone to create their own Non Volatile Memory Express (NVMe) Computational Storage Devices with readily available hardware platforms and open-source software.

What is computational storage ?

Computational Storage is a new processing paradigm, a new architecture, where storage devices that are capable performing computations are employed.

Computational Storage Devices (CSDs) allow to reduce the data bottleneck to the main processor. They also allow to scale processing capabilities with the amount of data.

CSDs can even perform computations during the main processor's downtime. They can be used for lengthy tasks such as video transcoding or AI model training.

Our approach to computational storage

Our computation storage devices are based on the Non-Volatile Memory Express (NVMe) open standard and present themselves as such to a computer. They can be used as a traditional NVMe SSD connected over PCIe.

We build them around hardware that is capable of running Linux and implement our NVMe firmware within. This allows for a very large range of hardware, we already support multiple platforms with different capabilities and hardware accelerators (e.g., GPU, FPGA, NPU, Video CODECs, etc.).

Computational functions can be activated through NVMe custom commands as well as TCP/IP tunneled over NVMe. This allows for easy integration and use of CSDs in already existing architectures.

List of supported hardware platforms

Our goal is to support a wide variety of readily available hardware in order to lower the barrier of entry to CSD development as much as possible. We have made it possible to run our CSD firmware on platforms ranging from expensive FPGA SoCs to cheap (sub 100$) off-the-shelf single board computers.

See the list of supported hardware in the platforms README.

NVME CSD Firmware

A Linux based Firmware for Hardware Agnostic NVMe Computational Storage Devices

This project provides an open-source firmware to build hardware agnostic NVMe computational storage devices.

The firmware is implemented as a Linux PCI endpoint function driver. https://docs.kernel.org/PCI/endpoint/pci-endpoint.html

This allows the firmware to run on any target hardware that supports Linux and provides a PCI endpoint controller driver.

The NVMe CSD firmware is based on a Linux NVMe PCI endpoint function under development which is based on an initial RFC by Alan Mikhak https://lwn.net/Articles/804369/

Directory structure

• firmware : Documentation about the firmware and code to run on the CSD
• host : User space code and documentation for the host computer
• pcb : Open-Hardware printed circuit boards
• platforms : Documentation for each platform and platform specific files (e.g., FPGA project)
• res : Other resources, mainly images, diagrams, pictures

Running the CSD on a platform

1) Follow the instructions in the chosen platform directory to build the kernel and RootFS and prepare the platform. 2) Connect the platform to the host computer via PCIe. 3) Start the CSD driver on the given platform with the following command :

sudo nvme-epf-script -q <number of queues> -l <backend storage block device> --threads <number of transfer threads> start

For example with a SATA SSD/HDD or USB flash drive attached as /dev/sda, or /dev/ram0 for a Linux RAM disk block device :

sudo nvme-epf-script -q 4 -l /dev/sda --threads 4 start

• It is possible to check for error messages or correct execution in the kernel log with dmesg.
• For automated start, write the command in a startup script e.g., with init.d. This way the CSD can start without manual intervention.

4) Turn on the host computer. 5) Verify that it recognized by the host computer. For this we recommend the NVMe command line utility tool https://github.com/linux-nvme/nvme-cli which can be installed through most package managers, e.g., on Ubuntu with sudo apt install nvme-cli.

sudo nvme list

Which will list all NVMe drives, e.g., a Samsung 970 and the CSD, listed as "Linux pci_epf".

Node                  SN                   Model                                    Namespace Usage                      Format           FW Rev  
--------------------- -------------------- ---------------------------------------- --------- -------------------------- ---------------- --------
/dev/nvme0n1          S4EWNM0TA08899W      Samsung SSD 970 EVO Plus 1TB             1         580.54  GB /   1.00  TB    512   B +  0 B   2B2QEXM7
/dev/nvme1n1          0df8d0659e3ecf8c2a94 Linux pci_epf                            1         500.11  GB / 500.11  GB    512   B +  0 B   6.5.0-rc

6) The CSD can be used as a normal disk. 7) For the computational capabilities and demos check the README in the host directory. 8) For SSH and adding the CSD to the host network check the host/socket_relay directory.

Information for developers

The global architecture is presented in the diagram below :

We will follow the diagram from top to bottom

• User space Application : These are host side applications that use the NVMe CSD, a few examples are given in the host/demos directory. Host side applications rely on the Compute Storage API to interact with the CSD. Another way to interact with the CSD is thanks to sockets over NVMe, e.g., one can connect over SSH over NVMe, for this check out the host/socket_relay directory.
• Compute Storage API : This is the main interface between user space applications and the CSD. The API is based on the SNIA Computational Storage API which can be found here. The API is defined in the cs.h file. The implementation depends on the CSD as it could be used on non NVMe CSDs as well. We have an implementation that implements several functions of the API the code is the cs_api_nvme_tsp.c file. (Note: the TSP acronym is Towards Computational Storage and was used during development). The API relies on libnvme to send custom commands to the NVME CSD.
• Libnvme : https://github.com/linux-nvme/libnvme allows to send custom commands to the native Linux NVMe driver. Mostly the nvme_admin_passthru() function is used. For other related functions and sending custom IO commands see https://github.com/linux-nvme/libnvme/blob/master/src/nvme/ioctl.h
• NVMe driver : This is the standard native Linux NVMe driver. https://elixir.bootlin.com/linux/latest/source/drivers/nvme/host
• PCIe Host Controller Driver : This is standard.
• PCIe Endpoint Controller Driver : This is the driver for the endpoint and allows the device to act as a PCIe endpoint device. There are several platforms that support this feature and have a driver. For more info see platforms/README.md. In the Linux kernel the drivers are here https://elixir.bootlin.com/linux/latest/source/drivers/pci/controller this directory both has root complex and endpoint controller drivers (on embedded devices the controller can often work in both modes). Most of the time the root complex controller driver is available (as this is the most used feature) but not the endpoint driver, so it might be needed to write one.
• Endpoint Function Driver : NVMe controller : This is the main part of the NVMe CSD, it is where most of the magic happens. This driver implements all the NVMe logic and custom commands. This driver is hardware agnostic thanks to the Linux PCIe endpoint framework and runs on the different platforms. It is the same file for all platforms, however for ease of build we directly included it in the Linux kernel trees for the different platforms. For a new platform you can copy the file from an existing platform. Note that it relies on a series of patches to the Linux PCIe endpoint framework to support some features not in the mainline kernel yet so these patches should also be included. In Linux the file is under drivers/pci/endpoint/functions/pci-epf-nvme.c. You can start with the kernel of one of the supported platforms and work from there for a new platform, the kernel for the RK3399 platforms is based on mainline Linux, the one for the Xilinx platform is based on linux-xlnx Linux.
• Custom Cmds : Custom admin and io commands are decoded in the driver above. Check the functions pci_epf_nvme_process_admin_cmd() and pci_epf_nvme_process_io_cmd() they will decode the custom opcodes and call the appropriate functions.
• Compute Thread : A kernel thread can be launched to do some asynchronous work on computational commands see the tsp_launch_async_compute() function in pci-epf-nvme.c.
• Computational App : It is possible to process custom compute NVMe commands in user space, this is done through command queues to and from user space, they are implemented as character devices (code in pci-epf-nvme.c). Reading gets a command and data and writing allows to return data and a completion. An example is available in firmware/crypt, see the README.

This serves as a very light overview of the code, if you are interested in development and have questions, please open an issue on github to start a discussion.