isolcpus=1,2,3 does not isolate on Raspberry Pi 4Bx4Gb 5.15.65-rt49/2.9 32bit

Like the title says, when I add " isolcpus=1,2,3 idle=poll " to the end of the string at /boot/cmdline.text.
I do not get 1-3 when I cat /sys/devices/system/cpu/isolated.

When I run latency-histogram --nobase I get "4 cores no_isolcpus ARMv7 Processor rev 3 (v71) as a header. 
min(us)-108.6, sdev(us) 2.2, max(us)121.5

If I run the histogram and open htop I can see all 4 cores bouncing the loads around.

Can anyone verify isolcpus is working on their Rpi4x4gb with this or higher PreemptRT kernel.
This was compiled in the weee hours of the night last night from a vanilla RaspiOS 32bit with the gnipsel "Installing LinuxCNC on Debian 11" instructions after loading the kdoren/linux/releases PreemptRT kernel patches.

The Pi is up and running, talking nice to my 7i90, but looking like Mt.Everest on my histogram.

Thoughts? Instructions?

kdoren's procedure puts all files in a separate folder that has the same name as the kernel release.
Indeed in the file /boot/config.txt you will find the command os_prefix=$KERN/ which in your case will be 5.15.65.rt65-v7l+.

Therefore you will need to edit the /boot/5.15.65.rt65-v7l+/cmdline.txt file.
In case it is not present, you can take the content of the one present in /boot/cmdline.txt and adapt it to your needs

in any case all the instructions and the link to the ready-made image are also available here:

forum.linuxcnc.org/9-installing-linuxcnc...erry-pi-3b-pi#260915

you can check cmdline the running kernel was started with with 'cat /proc/cmdline'

Sorry for not responding sooner guys, I have been blocked from the forum for "too many unsuccessful login attempts" not my fault, something to do with spam or hackers. On my cellphone's hotspot to post this.

I tried adding the isolcpus to the other cmdline.txt seems to have fixed me up.

Thanks guys!

I was tinkering trying to reduce latency on a pi3b  and found what looks like a similar issue with isolcpus

• Raspberry  pi 3b 
• I'm running Linux raspberry pi  5.15.84-v8+ #1613  SMP PREEMPT  aarch64 GNU-Linux
•  
• compiled Run in place  as I couldn't get debuild to complete
•  
• echo -n ' isolcpus=1,2,3 idle=poll processor.max_cstate=1' | sudo tee -a /boot/cmdline.txt
• checked all ok   
• from terminal cat /boot/cmdline.txt      isolcpus=1,2,3 idle=poll processor.max_cstate=1
•  
• from terminal launched latency-histogram 
  • from terminal it says Note:  using POSIX non-realtime  
  • in histogram is says 4 cores no_isolcpus

Regards
Nick

 

nickom44 wrote:

I was tinkering trying to reduce latency on a pi3b  and found what looks like a similar issue with isolcpus

• Raspberry  pi 3b 
• I'm running Linux raspberry pi  5.15.84-v8+ #1613  SMP PREEMPT  aarch64 GNU-Linux
•  
• compiled Run in place  as I couldn't get debuild to complete
•  
• echo -n ' isolcpus=1,2,3 idle=poll processor.max_cstate=1' | sudo tee -a /boot/cmdline.txt
• checked all ok   
• from terminal cat /boot/cmdline.txt      isolcpus=1,2,3 idle=poll processor.max_cstate=1
•  
• from terminal launched latency-histogram 
  • from terminal it says Note:  using POSIX non-realtime  
  • in histogram is says 4 cores no_isolcpus
    
    
    Regards
    Nick
    
    

What is the contents of the /boot/config.txt file?

The OS "Linux raspberry pi  5.15.84-v8+ #1613  SMP PREEMPT  aarch64 GNU-Linux" is not realtime

Hi elovalvo,

Here's the contents .

Regards
Nick

GNU nano 5.4 config.txt # uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable infrared communication.
#dtoverlay=gpio-ir,gpio_pin=17
#dtoverlay=gpio-ir-tx,gpio_pin=18

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

# Automatically load overlays for detected cameras
camera_auto_detect=1

# Automatically load overlays for detected DSI displays
display_auto_detect=1

# Enable DRM VC4 V3D driver
dtoverlay=vc4-kms-v3d
max_framebuffers=2

## Run in 64-bit mode
arm_64bit=1

# Disable compensation for displays with overscan
disable_overscan=1

[cm4]
# Enable host mode on the 2711 built-in XHCI USB controller.
# This line should be removed if the legacy DWC2 controller is required
# (e.g. for USB device mode) or if USB support is not required.
otg_mode=1

[all]

[pi4]
# Run as fast as firmware / board allows
arm_boost=1

[all]

nickom44 wrote:

• compiled Run in place  as I couldn't get debuild to complete
• from terminal launched latency-histogram 
  • from terminal it says Note:  using POSIX non-realtime  
  • in histogram is says 4 cores no_isolcpus

did you run "sudo make setuid" after building linuxcnc? without setuid bit rtapi_app doesn't have permission to get realtime scheduler priority.

nickom44 wrote:

Hi elovalvo,

Here's the contents .

Regards
Nick

From what I see missing any line of the type

kernel=vmlinuz-XXXXX

and therefore the operating system is not realtime.

If you want an image that definitely works on Raspberry Pi 3 you can use the one you find here: forum.linuxcnc.org/9-installing-linuxcnc...3b-pi?start=0#260915