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

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

elovalvo wrote:

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

 
you are right, the system isn't running the preempt-rt kernel.
proper uname (except for aarch64) should be Linux raspberrypi 5.15.65-rt49-v8+ #1 SMP PREEMPT_RT Tue Sep 6 18:12:35 BST 2022 aarch64 GNU/Linux