On Sat, Aug 13, 2022 at 08:01:02AM +0800, Li Hua wrote: > The problem that the statistical time goes backward, the value read first is 319, and the value read again is 318. As follows： > first： > cat /proc/stat | grep cpu1 > cpu1 319 0 496 41665 0 0 0 0 0 0 > then： > cat /proc/stat | grep cpu1 > cpu1 318 0 497 41674 0 0 0 0 0 0 > > Time goes back, which is counterintuitive. > > After debug this, The problem is caused by the implementation of kcpustat_cpu_fetch_vtime. As follows： > > CPU0 CPU1 > First: > show_stat(): > ->kcpustat_cpu_fetch() > ->kcpustat_cpu_fetch_vtime() > ->cpustat[CPUTIME_USER] = kcpustat_cpu(cpu) + vtime->utime + delta; rq->curr is in user mod > ---> When CPU1 rq->curr running on userspace, need add utime and delta > ---> rq->curr->vtime->utime is less than 1 tick > Then: > show_stat(): > ->kcpustat_cpu_fetch() > ->kcpustat_cpu_fetch_vtime() > ->cpustat[CPUTIME_USER] = kcpustat_cpu(cpu); rq->curr is in kernel mod > ---> When CPU1 rq->curr running on kernel space, just got kcpustat This is unreadable, what?!?
