Preempt-rt kernel build for beagleboard
Yu Pan <panyu2000@...>
I started looking at Yocto 2 weeks back. Despite the complexity in kernel building, I found it quite hard to locate information on preempt-rt build. I was trying to build linux-yocto-rt for beagleboard from "danny" and the linux-yocto-3.4 kernel, and it seems to be working. I'd like to share how one can do that in this thread.
Since the kernel does not include an official preempt-rt branch for beagleboard yet, I choose to directly use the standard/preempt-rt/base branch. I guess this should work for the preempt-rt kernel, from the fact that the standard kernel (non preempt-rt) used for beagleboard from the standard/beagleboard branch is basically identical to that from the standard/base branch.
Here is what I did.
1. Under poky/meta-yocto-bsp/recipes-kernel/linux, I added a linux-yocto-rt_3.4.bbappend recipe containing the following lines. The SRCREV value used is the same as the one in the base linux-yocto-rt_3.4.bb under poky/meta/recipes/kernel.
KBRANCH_beagleboard = "standard/preempt-rt/base"
SRCREV_machine_beagleboard ?= "5705c8037d2c47938034ead87c70ae3ebef552f7"
COMPATIBLE_MACHINE_beagleboard = "beagleboard"
2. Modified the PREFERRED_PROVIDER_virtual/kernel variable in poky/meta-yocto-bsp/conf/machine/beagleboard.conf to "linux-yocto-rt".
3. "bitbake linux-yocto-rt -c menuconfig" to set the Preemption Model to "Fully Preemptible Kernel (RT)".
4. "bitbake linux-yocto-rt"
5. "bitbake core-image-rt" which includes some realtime test programs on top of core-image-minimal.
I did some cyclictest on beagleboard using the generated kernel and image with "/usr/bin/cyclictest -p95 -m". The results did show huge improvement on max latency especially under load.
Hope it helps.