I just now compiled ppup1090 on Stretch image as per the method I have posted in thread How-to Feed Plane Plotter Site directly from Raspberry Pi
It’s normal CPU usage shown on top is less than 2%, but when I restarted dump1090-mutability, top started showing CPU usage 100%. The Performance Graphs show a jump in overall CPU usage from 15% to 35%.
After seeing this, I commented out line /home/pi/ppup/ppup-maint.sh & in file /etc/rc.local and rebooted Pi. The ppup1090 is no more running now.
EDIT:
The restart of dump1090-mutability was done manually by command sudo systemctl restart dump1090-mutability, and after observing its effect in top, command sudo pkill ppup1090 was issued. When ppup1090 restarted automatically after few seconds, the CPU usage returned to normal 2%
I also tested this by selecting a different gain value from drop-down list, then clicking “Set Gain” button. Result were same as with manual restart.