Linux Perf

Linux Perf

Linux software developers use perf to analyze performance.

Install and enable perf using the commands below. Make sure to become root where indicated.

For Ubuntu running on the Arm server run this command to install perf:

    

        
        
            sudo apt install linux-tools-common linux-tools-generic linux-tools-`uname -r` -y
        
    

For the Raspberry Pi 4 run this command:

    

        
        
            sudo apt-get install linux-perf	-y
        
    

Become root to enable access to the perf data:

    

        
        
            sudo su -
        
    

As root run the commands shown:

    

        
        
            echo -1 > /proc/sys/kernel/perf_event_paranoid
echo 0 > /proc/sys/kernel/kptr_restrict
        
    

Exit root:

    

        
        
            exit
        
    

If you don’t have the Linux source tree used in the Linux Kernel Compile section , retrieve it again using git:

    

        
        
            git clone --depth=1 https://github.com/raspberrypi/linux
        
    

In some cases, perf may not work on the Raspberry Pi 4 due to a mismatch between your running kernel and the linux-perf Debian package. To overcome this, build perf from source code.

Install the required tools for kernel building:

    

        
        
            sudo apt install git bc bison flex libssl-dev make
        
    

Build perf using make:

    

        
        
            cd linux
make -C tools/perf/
        
    

The perf command should now be available in the directory $HOME/linux/tools/perf

To list the available perf events:

    

        
        
            perf list
        
    

If you built perf from source in $HOME/linux list the events using:

    

        
        
            $HOME/linux/tools/perf/perf list
        
    

Linux perf works on both the Arm server and the Raspberry Pi 4. Arm servers have additional perf events because of the different processor type.

An example event which is included on the Arm server is stalled-cycles-backend. This event is not available on the Raspberry Pi 4.

Run a tar command to compress the Linux kernel source tree and count the stalled-cycles-backend event.

On the Arm server, run perf on a tar command to see the events.

    

        
        
            perf stat -e stalled-cycles-backend tar cfz test.tgz ./linux/
        
    

The expected output should be similar to:

    

        
         Performance counter stats for 'tar cfz test.tgz ./linux/':

    27,701,570,350      stalled-cycles-backend    #    0.00% backend cycles idle

      44.461783841 seconds time elapsed

      43.283230000 seconds user
       2.121127000 seconds sys

        
    

The Raspberry Pi doesn’t have the stalled-cycles-backend event.

    

        
        
            perf stat -e stalled-cycles-backend tar cfz test.tgz ./linux/
        
    

The expected output shows the stalled-cycles-backend is not available.

    

        
         Performance counter stats for 'tar cfz test.tgz ./linux/':

   <not supported>      stalled-cycles-backend

     143.177396310 seconds time elapsed

     129.623757000 seconds user
       8.292624000 seconds sys

        
    

Linux perf is available on the Arm server and the Raspberry Pi 4. The events are slightly different due to the processor, but perf generally works the same on both.