mingbo's tech tips

basically, when any process need to do I/O and underlying library calls io_schedule() will put CPU into iowait status and then if the CPU is idle (no other active process running), iowait time increases. below is related code snip from 3.x kernel: // in kernel/sched/cputime.c                                                                                                                                                                   /*  * Account for idle time.  * @cputime: the cpu time spent in idle wait  */ void account_idle_time(cputime_t cputime) {     u64 *cpustat = kcpustat_this_cpu->cpustat;     struct rq *rq = this_rq();                                      // get running queue of this processor/CPU     if (atomic_read(&rq->nr_iowait) > 0)                 // if there's process in iowait status         cpustat[CPUTIME_IOWAIT] += (__force u64) cputime;     else         cpustat[CPUTIME_IDLE] += (__force u64) cputime; } // in kernel/sched/cor