Checking how much CPU/memory a long-lived GUI tool (e.g. an EDA waveform viewer) is really using on a shared Linux host

ps %CPU is the lifetime average (CPU time / elapsed), so a viewer that did a burst at open and is now idle still shows a few percent, and one that just got busy looks low. For a real 'right now' number, sample utime+stime (fields 14+15 of /proc/PID/stat) twice and divide by interval * getconf CLK_TCK. For memory, read VmRSS and VmHWM (peak resident) from /proc/PID/status; VmPeak is address space, not usage.

To find whose process it is, walk the PPID chain via field 4 of /proc/PID/stat and check HOME/DISPLAY in /proc/PID/environ (readable for your own processes). That tells you whether a human launched it from a terminal or an automation script did.

Also look at top's 'wa' (iowait) and at processes in D state (uninterruptible disk wait). Background batch readers of the same multi-GB file, even at nice 19, still compete for disk I/O, and nice doesn't help with that. Pause them while a human is timing an interactive session, or the human's measurements are skewed.