A kernel module to tag stream ID to Linux block I/O requests based on Multi-stream. However, please be aware that Multi-stream is removed from Linux kernel since v5.18.
To compile and install this module as a Linux Kernel module, just run make.
Before loading the kernel module, please check if your SSD supports stream and your OS has enabled stream capability as described in the first two sections of this README. For the usage of the kernel module, see "Enable the Kernel Module and Assign Processes to Them" and "Change Kernel Module Parameters On-the-fly".
sudo nvme dir-receive /dev/nvme0n1 -D 1 -O 1 -H
-D is type and -O is operation. Both = 1 will ask for stream support of this controller (defined in NVMe protocol). -H is to make the result human readable. This can show if the SSD has stream support and maximum number of streams supported by the SSD.
This is to enable the stream capability in Linux Kernel.
- Edit /etc/default/grub, add "nvme_core.streams=1" to
GRUB_CMDLINE_LINUX. - Run
sudo update-grubto update grub settings. - Reboot.
sudo modprobe streamidtag streams="a;b,c;d,e,f"
The kernel module accepts a parameter, namely "streams", as a list of processes to be assigned to different streams. To separate streams, use semicolon (;). To separate processes in streams, use comma (,). Trailing semicolons can be skipped (i.e.: ";;d,e,f" is equivalent to ";;d,e,f;").
In this example, it will set parameter streams of module streamidtag to "a;b,c;d,e,f", which asks the kernel module to assign all write requests by process a to stream 2, all write requests by process b and c to stream 3, and d, e, f to stream 4. Stream 5 has no process assigned.
You can add at most 16 streams. Linux Kernel supports at most four streams, but the Multi-stream feature supports more streams as defined in the NVMe protocol. This kernel module circumvents the limit given by the kernel by setting the ctrl->nr_streams to 17. Stream ID in Linux starts from 2, so the streams ranges from 2 to 17. FYI, stream 0 is WRITE_LIFE_NOT_SET and stream 1 is WRITE_LIFE_NONE, and they will both be passed as 0 to the SSD - other stream numbers will decrease by 1 (ref: see drivers/nvme/host/core.c).
Similarly, ";;d,e,f;" means assign all write requests by d, e, f to stream 4, and do not assign any write requests by any processes to stream 2, 3, or 5.
If you have already loaded the kernel module, but want to change the processes assigned to each write stream, you can use the following command:
echo "g;h;a,b,c" | sudo tee /sys/module/streamidtag/parameters/streams
This will set parameter streams of module streamidtag to "g;h;a,b,c".