Re: [Crash-utility] [PATCH v2] ps: Add support to "ps -l|-m" to properly display process list
Hi Austin,
-----Original Message-----
> > This is because output of "ps -l|-m" depends on
task_struct.sched_info.last_arrival.
> >
> > Without CONFIG_SCHEDSTATS or CONFIG_SCHED_INFO, 'sched_info' field is
not included
> > in task_struct.
> >
> > So we make "ps -l|-m" option to access 'exec_start' field of
sched_entity
> > where 'exec_start' is task_struct.se.exec_start.
>
> Could you describe what the exec_start means? When is it updated?
>
The 'task_struct.se.exec_start' contains the most recently-executed
timestamp when
process is running in the below cases;
- enqueued to runqueue
- dequeued from ruqueue
- scheduler tick is invoked
- etc
So I guess 'task_struct.se.exec_start' could be one of statistics
which indicates
the most recently run timestamp of process activity.
From CFS scheduler's point of view, 'task_struct.se.exec_start' is
updated within update_curr()
where its call path is various as below.
- enqueue_task_fair, -dequeue_task_fair, task_tick_fair,
check_preempt_wakeup, ...
Thank you for looking into this.
As for when the se.exec_start is updated, I think you are right.
(with my understanding, probably it's the last time or tick when a task
is in a runqueue regardless of getting a CPU.)
But I found a problem, is that the se.exec_start is from rq->clock_task,
not from rq->clock like last_arrival. The rq->clock_task may not contain
irq/steal time, please see update_rq_clock_task().
This causes the following issues with a vmcore generated on a machine,
which had run for a while (273 days):
crash> ps -m | head
[ 0 00:59:36.582] [RU] PID: 4023608 TASK: ffff916f7c6b1840 CPU: 15 COMMAND:
"makedumpfile"
^^^^^^^^^(1)
[ 0 00:59:37.831] [ID] PID: 413 TASK: ffff916f772d3080 CPU: 15 COMMAND:
"kworker/15:1H"
[ 0 00:59:39.765] [IN] PID: 3929504 TASK: ffff916f5f0748c0 CPU: 15 COMMAND:
"respawn_actlog"
[ 0 00:59:40.650] [IN] PID: 1974 TASK: ffff91647dc53080 CPU: 15 COMMAND: "CPU
2/KVM"
[ 0 00:59:41.925] [IN] PID: 1297 TASK: ffff916f63c46100 CPU: 15 COMMAND:
"NetworkManager"
[ 0 00:59:42.944] [ID] PID: 3763057 TASK: ffff9160c4519840 CPU: 15 COMMAND:
"kworker/15:0"
[ 0 00:59:42.944] [IN] PID: 101 TASK: ffff916040c91840 CPU: 15 COMMAND:
"migration/15"
[ 0 00:59:43.078] [IN] PID: 100 TASK: ffff916040c5b080 CPU: 15 COMMAND:
"watchdog/15"
[ 0 00:59:47.533] [IN] PID: 1292 TASK: ffff916f63c43080 CPU: 15 COMMAND:
"lsmd"
[ 0 00:59:49.089] [IN] PID: 113105 TASK: ffff9160412248c0 CPU: 15 COMMAND:
"kvm-nx-lpage-re"
^^^^^^^(2)
(1) large difference from zero
(2) large differences among CPUs (probably due to the differences of irq time)
(1) might be solved with rq->clock_task, but (2) will be misleading and confusing.
So currently I'm thinking that the "ps -l|-m" options should not use the
se.exec_start.
What do you think?
Thanks,
Kazu