Insufficient Data Collection

Symptom

When using the tool to analyze false sharing, the collected data may be significantly lower than expected and incomplete.

Possible Causes

The CPU idle management driver is enabled in the current environment, and the CPU may enter deep idle states, resulting in insufficient data being collected by the tool.

Troubleshooting Procedure

Run the following command to check the driver status:
```
cat /sys/devices/system/cpu/cpuidle/current_driver
```
If the command output is acpi_idle, go to 2. If the command output is none, the issue is irrelevant to the driver configuration. You are advised to collect data again or increase the collection duration.
Use either of the following methods to modify the driver configuration. Method 1 is preferred because it does not require restarting the OS.
- Method 1: Before collecting data, run the following command to temporarily disable the CPU from entering deep idle states:
```
for f in $(find /sys/devices/system/cpu -path "*/cpuidle/state*/disable" ! -path "*/state0/*"); do
    echo 1 > "$f"
done
```
  After the collection is complete, run the following command to restore the configuration:
```
for f in $(find /sys/devices/system/cpu -path "*/cpuidle/state*/disable" ! -path "*/state0/*"); do
    echo 0 > "$f"
done
```
- Method 2: Enter the system BIOS settings, as shown in Figure 1. Find the CPU PM Control option, as shown in Figure 2.
  Figure 1 BIOS settings
  
  Figure 2 CPU PM Control
  
  Disable the Low Power Idle (LPI) option, as shown in Figure 3. Save the BIOS configuration and restart the system.
  Figure 3 LPI
  
  After step 2 is completed, the CPU will no longer enter deep idle states, which helps improve the completeness and stability of the data collected by the tool. However, this may increase system idle power consumption and temperature. It is recommended to enable this setting only during performance data collection or troubleshooting, and restore the original BIOS configuration or run commands to restore the original configuration afterward if needed.

Parent topic: FAQs