High Load when reading from virtual COM port

[lifthanger]

Dear KUNBUS-Support,

I'm using a RevPI Connect 4 with the most recent stable Image and and up-to-date system and kernel.
My application reads about 250kB/s from a device that presents as a virtual COM port over USB.

dmesg - snippet

Code: Select all

[ 6809.763018] usb 1-2: new full-speed USB device number 6 using xhci_hcd
[ 6810.170930] usb 1-2: Product: STM32 Virtual ComPort
[ 6810.170931] usb 1-2: Manufacturer: STMicroelectronics
[ 6810.189710] cdc_acm 1-2:1.0: ttyACM0: USB ACM device

This leads to a very high CPU load and subsequent data loss because of the process "irq/34-xhci_hcd" similar to viewtopic.php?t=4225. Interrupts caused by xhci are about 45000 per second.

With piControl already disabled and without desktop environment running, the system load averages at about 3.2 while reading from USB.
On a standard raspberry pi 4b with Raspberry Pi OS the same application averages a load of about 1.0.

I wanted to try the 6.6 Kernel using the instructions for 6.1 from your kernelbakery, but the Makefile seems to be missing a target.

Unfortunately the RevPi would not be usable for my application in this state.
Is there some way to mitigate this problem?
Thanks!

[dirk]

Hello lifthanger, I am interested to see your message. Now the new RevPi Bookworm OS has been released see here:
https://revolutionpi.com/forum/viewtopic.php?t=4524
Can you test your setup again with the new RevPi Bookworm OS?