Desktop freezing for 1 second every 30 seconds

I have a Pi4 (a 4té2) since a few weeks and I have not yet been able to track down the problem. It is not annoying in daily work, you just notice a slight resistance/delay in some actions, but it is clearly visible while playing music in DigitalCD along with visual plugins.

For some reason, every 30 seconds the animation freezes, but the problem disappear under higher CPU like when playing a video.
It is not linked to a particular application, and I once killed all non-ROM modules without being able to affect the problem.

Since CPU usage affects the issue, could this be related to the system trying to reduce the CPU clock when it thinks the system is barely active?

Try running !CPUClock you may see the CPU clock on the icon bar change at that point, if not you can set it up to log to a file.

every 30 seconds the animation freezes, but the problem disappear under higher CPU like when playing a video

I’ve previously seen performance issues like this and worked around it by wrapping intensive tasks with:

   MOV     R0, #0
   MOV     R1, #0
   SWI     XPortable_Speed		;force CPU to full speed
   STR     R0, [R13, #-4]!		;and stack old state
...do stuff
   LDR     R0, [R13], #4		;get old state from stack
   MOV     R1, #0
   SWI     XPortable_Speed		;set CPU speed back

CPUClock always showed 1800 MHz but I cannot tell what happens during 1 second freeze.

I have now created a little basic application which counts to 2000 on each Wimp_Poll (not PollIdle) to get rid of that issue.

I have now created a little basic application which counts to 2000 on each Wimp_Poll (not PollIdle) to get rid of that issue.

?
Probably I misunderstand it, but to me this solution is like punching your stomach to get distracted from your headache.

My 4té had the behaviour that you described, although I haven’t noticed it any more since a while. My 4té2 never had this. But I’ll keep an eye open.

Probably I misunderstand it, but to me this solution is like punching your stomach to get distracted from your headache.

Keyboard, mouse and other event take priority so at max you are delayed by a single Null Event of this little “Poll” application which takes maybe a millisecond so it won’t be noticed.

The Wimp sends a null event to each application in turn, just skipping applications where a monotonic time specified with Wimp_PollIdle is not reached yet, so in the same way it cannot really affect other applications. In other words there is just an accumulation of null events for the “Poll” application when other applications are idle, you consume a little more CPU and increase the temperature of the 4té2 from 49 to 50/51 degrees. Big deal! I would maybe hesitated to do this on the Pi3 as it operates at much higher temperatures, but here I don’t even have to activate the fan.