It's unreadable, I'm sorry about that. The CPU statistics time read from /proc/stat should only be incremented. The bug I found is that the value read latest is smaller than the former. The root cause of the problem is that the "vtime->utime" and "delta" are temporarily added to the stack and show to the user. The value of 'vtime->utime + delta' depends on which task the CPU is executing. As bellow: show_stat -> kcpustat_cpu_fetch -> kcpustat_cpu_fetch_vtime -> cpustat[CPUTIME_USER] += vtime->utime + delta
