EBC Exercise 36 PREEMPT RT
Embedded Linux Class by Mark A. Yoder
Here are instructions on how to install a PREEMPT_RT Kernel and run some tests on it.
Contents
Installing a PREEMPT_RT Kernel
To install a real time kernel, first see what you are currently running.
bone$ uname -a Linux ece434 4.19.94-ti-r45 #1buster SMP PREEMPT Thu Jun 18 19:18:41 UTC 2020 armv7l GNU/Linux
Also do the following.
bone$ head /boot/uEnv.txt #Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0 uname_r=4.19.94-ti-r45 #uuid= #dtb=
Note what uname is set to. You'll want to return to it when you are done.
Now, look for a real time kernel with similar number.
bone $ cd /opt/scripts/tools bone$ ssudo ./update_kernel.sh --bone-rt-kernel info: checking archive 2020-08-06 15:12:44 URL:https://rcn-ee.com/repos/latest/buster-armhf/LATEST-bone-rt [195/195] -> "LATEST-bone-rt" [1] ----------------------------- Kernel Options: ABI:1 LTS44 4.4.145-bone-rt-r23 ABI:1 LTS49 4.9.178-bone-rt-r15 ABI:1 LTS414 4.14.185-bone-rt-r37 ABI:1 LTS419 4.19.127-bone-rt-r53 ABI:1 LTS54 5.4.52-bone-rt-r31 ABI:1 STABLE 5.6.17-bone-rt-r14 ----------------------------- Kernel version options: ----------------------------- LTS414: --lts-4_14 LTS419: --lts-4_19 LTS54: --lts-5_4 STABLE: --stable TESTING: --testing ----------------------------- Please pass one of the above kernel options to update_kernel.sh -----------------------------
I'm running at 4.19 kernel. The highlighted line above (4.19.127-bone-rt-r53) is the most current version of the 4.19 real time kernel. Let's install it.
bone$ sudo ./update_kernel.sh --kernel 4.19.127-bone-rt-r53 ...
After a couple of minutes the new kernel is installed. (Mine took some 2.5 minutes.) Look in /boot
bone$ ls /boot config-4.19.127-bone-rt-r53 initrd.img-4.19.94-ti-r45 uboot vmlinuz-4.19.94-ti-r45 config-4.19.94-ti-r45 SOC.sh uEnv.txt dtbs System.map-4.19.127-bone-rt-r53 uEnv.txt.orig initrd.img-4.19.127-bone-rt-r53 System.map-4.19.94-ti-r45 vmlinuz-4.19.127-bone-rt-r53
You see both the original kernel and the one just installed. The file uEnv.txt tells which one to boot from:
bone head /boot/uEnv.txt #Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0 uname_r=4.19.94-ti-r45 #uuid= #dtb=
You see it's been changed to boot the new kernel. But don't reboot just net. Let's take some measurements.
Measure the latency
Before rebooting let's measure the non-rt latency.
bone$ cd ~/exercises/linux/kernel/rt bone$ sudo apt install rt-tests
(Check install.sh for latest instructions of what to install.) Now run the test:
bone$ time sudo ./hist.gen > nort.hist
If you get an error:
Unable to change scheduling policy! Probably missing capabilities, either run as root or increase RLIMIT_RTPRIO limits
try running ./setup.sh. If that doesn't work try:
bone$ sudo bash bone# ulimit -r unlimited bone# ./hist.gen > nort.hist bone# exit
This sets the maximum real-time scheduling priority to unlimited.
While hist.gen is running, open another window on the bone and run some time intensive tasks. Here's what I did.
bone$ cd ~/exercises/linux/modules bone$ make bone$ make clean
Repeat the two make commands until hist.gen finishes. This will take a while. Here are the times I got for hist.gen.
real 1m40.222s user 0m0.938s sys 0m7.767s
This creates a histogram data file 'nort.hist. Now you can reboot into the rt kernel.
bone$ sudo reboot
After rebooting you will see.
bone$ uname -a Linux beaglebone 4.14.52-ti-rt-r60 #1 SMP PREEMPT Tue Jun 26 23:28:55 UTC 2018 armv7l GNU/Linux
Now repeat the test.
bone$ cd ~/exercises/linux/kernel/rt bone$ time sudo ./hist.gen > rt.hist
Again, do the same time intensive things in another window.
Once the test is done, go to your host computer to generate the plots. (There's less to install than on the bone.
Let's mount the bone's files on the host so they are easy to get to.
host$ cd host$ mkdir bone host$ sudo apt update host$ sudo apt install sshfs host$ sshfs bone:. bone
This says to mount the home directory on the bone (bone:.) on the local directory, called bone, on the host. Now change to that directory.
host$ cd bone/exercises/linux/kernel/rt host$ ls hist.gen hist.plt install.sh nort.hist rt.hist setup.sh
You should now see the files you just generated on the bone.
host$ sudo apt install gnuplot host$ gnuplot hist.plt
This will generate the file cyclictest.png which contains your plot.
host$ xdg-open cyclictest.png
This will display your cyclictest.png file. Mine looks something like:
Returning to the non-rt kernel
You can return to the non-rt kernel that you running before by editing /boot/uEnv.txt and returning uname_r to what it originally was and then rebooting.
To view the old kernel version you can look into the /boot directory.
bone$ ls /boot
bone$ sudo nano /boot/uEnv.txt uname_r=4.14.52-ti-r60
bone$ sudo reboot
You should now be back to where you started.
Installing a PREEMPT_RT Kernel Alternate way
This is a set of instructions for installing the RT kernel. They are an alternate way from what was shown above. They are here for completeness. No need to install again.
To install a real time kernel, first see what you are currently running.
bone$ uname -a Linux beaglebone 4.14.52-ti-r60 #1 SMP PREEMPT Tue Jun 26 23:02:46 UTC 2018 armv7l GNU/Linux
Also do the following.
bone$ head /boot/uEnv.txt #Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0 uname_r=4.14.52-ti-r60 #uuid= #dtb=
Note what uname is set to. You'll want to return to it when you are done.
Now, look for a kernel with similar number.
bone$ sudo apt update bone$ apt-cache search linux-image-4.14 > /tmp/search
Look through /tmp/search and pick an image with -rt- in it's name.
bone$ grep 14.52 /tmp/search linux-image-4.14.52-armv7-lpae-x3 - Linux kernel, version 4.14.52-armv7-lpae-x3 linux-image-4.14.52-armv7-rt-x4 - Linux kernel, version 4.14.52-armv7-rt-x4 linux-image-4.14.52-armv7-x4 - Linux kernel, version 4.14.52-armv7-x4 linux-image-4.14.52-bone-rt-r16 - Linux kernel, version 4.14.52-bone-rt-r16 linux-image-4.14.52-bone16 - Linux kernel, version 4.14.52-bone16 linux-image-4.14.52-ti-r59 - Linux kernel, version 4.14.52-ti-r59 linux-image-4.14.52-ti-r60 - Linux kernel, version 4.14.52-ti-r60 linux-image-4.14.52-ti-r61 - Linux kernel, version 4.14.52-ti-r61 linux-image-4.14.52-ti-rt-r59 - Linux kernel, version 4.14.52-ti-rt-r59 linux-image-4.14.52-ti-rt-r60 - Linux kernel, version 4.14.52-ti-rt-r60 linux-image-4.14.52-ti-rt-r61 - Linux kernel, version 4.14.52-ti-rt-r61
bone$ sudo apt install linux-image-4.14.52-ti-rt-r60 Reading package lists... Done Building dependency tree Reading state information... Done Suggested packages: linux-firmware-image-4.14.52-ti-rt-r60 The following NEW packages will be installed: linux-image-4.14.52-ti-rt-r60 ... Setting up linux-image-4.14.52-ti-rt-r60 (1stretch) ... update-initramfs: Generating /boot/initrd.img-4.14.52-ti-rt-r60 zz-uenv_txt: Updating /boot/uEnv.txt [uname_r=-4.14.52-ti-rt-r60]
Mine took some 2.5 minutes.
Embedded Linux Class by Mark A. Yoder