x86 LBR Collection Tool

simple-pebs is an x86 (Intel) Linux kernel module that collects branch information (LBR) using PEBS + LBR and writes samples into a per-CPU output buffer. The data is exposed to user space via /dev/simple-pebs.

Requirements

Kernel build directory must exist:
- /lib/modules/$(uname -r)/build
Root privileges are required to load kernel modules.
- In containers, run with --privileged.
Supported environments:
- Linux kernel 5.4 only.
- The CPU must support the required PMU features (PEBS / LBR).

Tested CPU:

Emerald Rapids (Architectural LBR)

To add support for a new CPU model, add its model ID in the check_cpu() function in the driver source.

Build

cd tools/lbr_driver
make

Install

sudo make install
sudo depmod -a
sudo modprobe simple-pebs

Or, in a debug environment:

sudo insmod simple-pebs.ko

Check

Confirm the device exists:

test -c /dev/simple-pebs && echo "OK"

Check dmesg:

dmesg | tail -n 200 | grep -i pebs

You should see output similar to:

[14725.398928] simple_pebs: Adaptive PEBS (v4) detected
...
[14725.587040] simple_pebs: cpu20 PEBS_DATA_CFG=1f000008 (lbr_depth=32)
[14725.587040] simple_pebs: 72: allocate_buffer: status 0 ctrl 0 counter 0
...
[14725.587040] simple_pebs: Initialized

Uninstall

sudo modprobe -r simple-pebs

Or, in a debug environment:

sudo rmmod simple-pebs

Usage

Build the libkperf tool first:

bash build.sh

The LBR collection demo is documented in: libkperf/docs/Details_Usage/采集BRBE数据

Current limitations:

PID and CPU filtering is not supported.
Only collect pmu 'cycles' event.
The tsc time in output data is rdtsc time, which is different from the ts in PMU collection.

To change the sampling period, modify the PERIOD value in the driver source code and rebuild the module.

To Configuring the branch event, modify the ctl in setup_arch_lbr function.