----- Original Message ----- They are different entities. The jiffies value is the number of ticks that have occurred since the system booted, incremented by one during each timer interrupt, which occur "HZ" times per second. On an x86_64 with a CONFIG_HZ of 1000, you can see it incrementing on a live system: crash> repeat -1 p jiffies jiffies = $4 = 4890813048 jiffies = $5 = 4890814058 jiffies = $6 = 4890815067 jiffies = $7 = 4890816077 jiffies = $8 = 4890817087 jiffies = $9 = 4890818097 jiffies = $10 = 4890819107 The task_struct.sched_info.last_arrival value is a 64-bit timestamp value that is taken from the task's per-cpu runqueue.clock. It gets set in the kernel here: static void sched_info_arrive(struct rq *rq, struct task_struct *t) { unsigned long long now = rq_clock(rq), delta = 0; if (t->sched_info.last_queued) delta = now - t->sched_info.last_queued; sched_info_reset_dequeued(t); t->sched_info.run_delay += delta; t->sched_info.last_arrival = now; t->sched_info.pcount++; rq_sched_info_arrive(rq, delta); } The per-cpu rq->clock 64-bit nanosecond-based timestamp can be watched on a live system for a particular cpu. For example: crash> runq CPU 0 RUNQUEUE: ffff88021e214040 CURRENT: PID: 0 TASK: ffffffff81c13440 COMMAND: "swapper/0" RT PRIO_ARRAY: ffff88021e2141c0 [no tasks queued] CFS RB_ROOT: ffff88021e2140d8 [no tasks queued] ... Taking cpu 0's rq address of ffff88021e214040 above, you can get a rough approximation showing that its clock advances 1000000000 times a second: crash> repeat -1 rq.clock ffff88021e214040 clock = 596217293435441 clock = 596218400742837 clock = 596219506034449 clock = 596220606332511 clock = 596221706630214 clock = 596222807928565 clock = 596223913227970 clock = 596225016526769 clock = 596226128827938 clock = 596227241129325 clock = 596228351913056 ... Dave