bootargs

I am trying to boot the kernel with isolcpus=0 in an attempt to improve latency with the Xenomai kernel.

As far as I can tell the way to do this with u-Boot is to edit the environement, ie "setenv bootargs isolcpus=0"

setenv is "Command Unknown" in the standard shell, so I have concluded that this needs to be done in the serial boot shell. (Right or wrong?)

But this doesn't seem to work:

printenv > bootargs=isolcpus=0 xeno_hal.supported_cpus=1

cat /proc/cmdline > console=ttymxc1,115200 root=/dev/mmcblk0p1 rootwait rw fbmem=24M video=mxcfb0:dev=hdmi,1920x1080M@60,bpp=32

(dmesg looks the same).

So, if editing bootargs _isn't_ the way to add a kernel boot parameter, what is the way?

On IRC I was told to "recompile the kernel with the right options" but I thought I would seek a second opinion before taking the step of figuring out what the "right options" are.

 

Hi,
to change boot environment you need to connect to your uDoo through serial boot console.
If all is ok, when you power on the board you'll see on the console u-boot startup, and a short countdown before kernel starts.
Stopping the countdown you will gain a minimal u-boot console. There you can set the new bootargs typing (it's a single line):

setenv bootargs 'console=ttymxc1,115200 root=/dev/mmcblk0p1 rootwait rw fbmem=24M video=mxcfb0:dev=hdmi,1920x1080M@60,bpp=32 isolcpus=0 xeno_hal.supported_cpus=1'

then:
boot

After that you have test the new environment, fix it with typing following commands (it's a single line):

setenv bootargs 'console=ttymxc1,115200 root=/dev/mmcblk0p1 rootwait rw fbmem=24M video=mxcfb0:dev=hdmi,1920x1080M@60,bpp=32 isolcpus=0 xeno_hal.supported_cpus=1'
saveenv

Bye
giuseppe

 

I eventually figured out two things:
1) Serial Tools on Mac is not the best tool for working at the serial terminal, it does not do terminal emulation, so "env edit bootargs" (for example) does not work. Better (on mac) is "screen /dev/tty.SLAB_USBtoUART 155200" at the terminal prompt, then things are a lot more "normal"
2) bootargs is over-written by mmcargs which is run by the boot script. "env edit mmcargs" seems to allow one to add boot args (possibly only when booting from ssd)