Configure tcm_loop device parameters-Alibaba Cloud Linux(Alinux)-阿里云帮助中心

When you use the Target Core Module in Userspace (TCMU) framework to implement userspace Internet Small Computer Systems Interface (iSCSI) targets, the default tcm_loop module parameters may not deliver optimal I/O performance for your workload. This document explains how to view and configure tcm_loop device parameters in Alibaba Cloud Linux 3 to tune I/O throughput in collaboration with the userspace backend.

Prerequisites

Before you begin, make sure that you have:

Alibaba Cloud Linux 3 as the operating system
Kernel version 5.10.134-17 or later

tcm_loop device parameters

The tcm_loop module exposes four parameters that control I/O queue depth and scatter-gather behavior. Parameter configurations apply to all tcm_loop devices.

Parameter	Description	Default value
`nr_hw_queues`	Number of hardware queues of a tcm_loop device	1
`can_queue`	Queue depth of each hardware queue	1024
`cmd_per_lun`	Maximum number of commands a Small Computer System Interface (SCSI) device can run per logical unit number (LUN)	1024
`sg_tablesize`	Maximum size of the scatter-gather table for a tcm_loop device	256

View tcm_loop device parameters

Load the tcm_loop module.
```
sudo modprobe tcm_loop
```

Read the current parameter values from sysfs.

cat /sys/module/tcm_loop/parameters/nr_hw_queues
cat /sys/module/tcm_loop/parameters/can_queue
cat /sys/module/tcm_loop/parameters/cmd_per_lun
cat /sys/module/tcm_loop/parameters/sg_tablesize

Configure tcm_loop device parameters

There are two ways to configure tcm_loop device parameters:

Method 1: Pass parameters when loading the module
Method 2: Use a configuration file

Method 1: Pass parameters when loading the module

If the tcm_loop module is already loaded, remove it first.
```
sudo modprobe -r tcm_loop
```

Load the module with the parameter values you want.

Replace the placeholders with the values you want to set.

sudo modprobe tcm_loop nr_hw_queues=<nr_hw_queues> can_queue=<can_queue> cmd_per_lun=<cmd_per_lun> sg_tablesize=<sg_tablesize>

Example — set nr_hw_queues to 4, can_queue to 2048, cmd_per_lun to 2048, and sg_tablesize to 512:

sudo modprobe tcm_loop nr_hw_queues=4 can_queue=2048 cmd_per_lun=2048 sg_tablesize=512

Verify

Confirm that the parameter values have taken effect.

cat /sys/module/tcm_loop/parameters/nr_hw_queues
cat /sys/module/tcm_loop/parameters/can_queue
cat /sys/module/tcm_loop/parameters/cmd_per_lun
cat /sys/module/tcm_loop/parameters/sg_tablesize

Method 2: Use a configuration file

If the tcm_loop module is already loaded, remove it first.
```
sudo modprobe -r tcm_loop
```

Create a configuration file in /etc/modprobe.d/.

Replace the placeholders with the values you want to set. The file must have a .conf extension.

sudo bash -c "cat > /etc/modprobe.d/<tcm_loop.conf> << EOF
options tcm_loop nr_hw_queues=<nr_hw_queues> can_queue=<can_queue> cmd_per_lun=<cmd_per_lun> sg_tablesize=<sg_tablesize>
EOF"

Example — create /etc/modprobe.d/tcm_loop.conf with nr_hw_queues=4, can_queue=2048, cmd_per_lun=2048, and sg_tablesize=512:

sudo bash -c "cat > /etc/modprobe.d/tcm_loop.conf << EOF
options tcm_loop nr_hw_queues=4 can_queue=2048 cmd_per_lun=2048 sg_tablesize=512
EOF"

Load the tcm_loop module.
```
sudo modprobe tcm_loop
```

Verify

Confirm that the parameter values have taken effect.

cat /sys/module/tcm_loop/parameters/nr_hw_queues
cat /sys/module/tcm_loop/parameters/can_queue
cat /sys/module/tcm_loop/parameters/cmd_per_lun
cat /sys/module/tcm_loop/parameters/sg_tablesize