Lightweight CPU isolation enables dynamic CPU isolation based on the system load and user configuration. The kernel migrates the tasks and interrupts from the isolated CPU to other CPUs for execution. The isolated CPU enters the idle state, which reduces the power consumption. In addition, user-mode configuration and query APIs are provided for better system optimization.
## Configuration
### Enabling Lightweight CPU Isolation
Enable related configuration items and dependencies.
To enable lightweight CPU isolation, you need to enable the corresponding configuration items and dependencies during kernel compilation. The related configuration items are as follows:
```
CONFIG_CPU_ISOLATION_OPT=y
CONFIG_SCHED_CORE_CTRL=y
```
Enable the following dependencies:
```
CONFIG_SMP=y
CONFIG_SCHED_WALT=y
```
## Available APIs
APIs are provided to set the number of isolated CPU cores and record the current status. Configurations can be performed based on CPU clusters. These APIs are located in the first CPU device directory of each CPU cluster, for example, `/sys/devices/system/cpu/cpu0/core_ctl`.
The Related Thread Group (RTG) provides optimized scheduling of a group of important threads. The load of an RTG can be collected and predicted separately and the preferred CPU cluster can be set to allow the important threads to run on the optimal CPU and the kernel to select a proper CPU frequency based on the group loads.
## Configuration
### Enabling RTG
To enable RTG, you need to enable the related configuration items and dependencies during kernel compilation. The related configuration items are as follows:
```
CONFIG_SCHED_RTG=y
CONFIG_SCHED_RTG_DEBUG=y
CONFIG_SCHED_RTG_FRAME=y
CONFIG_SCHED_RTG_RT_THREAD_LIMIT=y
```
Enable the following dependencies:
```
CONFIG_SCHED_WALT=y
```
### Adding a Process or Thread to an RTG
By default, 20 RTGs are created in the kernel. The group with ID of 1 is reserved and cannot be added with any process or thread.
```Bash
// Add a process to an RTG.
echo 2 > /proc/<pid>/sched_group_id
// Remove a process from an RTG. The group with ID of 0 is not an RTG.
echo 0 > /proc/<pid>/sched_group_id
```
### Obtaining RTG Information
The RTG information includes group ID, preferred CPU cluster ID, and thread information.
```Bash
cat /proc/sched_rtg_debug
// The following information is displayed:
RTG_ID : 2 // RTG ID.
RTG_INTERVAL : UPDATE:8ms\#INVALID:4294ms // CPU frequency modulation interval and valid load duration.
RTG_CLUSTER : -1 // CPU cluster ID. The value **-1** means that the preferred cluster is not set.
RTG_THREADS: 0/1 // Total number of threads in the group.
STATE COMM PID PRIO CPU // Thread information, including the status, name, PID, priority, and CPU ID.
