On Tue, 29 Mar 2016 16:12:38 -0300 Daniel Bristot de Oliveira <bris...@redhat.com> wrote:
> On 03/29/2016 02:13 PM, Steven Rostedt wrote: > >> <idle>-0 [007] d..3 78377.688969: sched_switch: > >> prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=b > >> next_pid=18973 next_prio=-1 > >> > b-18973 [007] d..3 78377.688979: sched_deadline_block: > >> > now=78377.688976271 deadline=78377.718945137 remaining_runtime=9968866 > >> > b-18973 [007] d..3 78377.688981: sched_switch: > >> > prev_comm=b prev_pid=18973 prev_prio=-1 prev_state=S ==> > >> > next_comm=swapper/7 next_pid=0 next_prio=120 > > Why did it go to sleep? The above is still not very useful. What do you > > mean "blocking on a system call"? > > A task can go can to sleep in a blocking system call, like waiting > a network packet, or any other external event. Note, waiting for a network packet or some other external event is a userspace call. A schedule out in 'S' state means exactly that. But I hate the term "blocked" because that is more like waiting for something else to finish (like blocked on a lock). In which case, if that did happen, the state would be "D" not "S". "S" is basically "sleeping" and it gets woken up by some other event. A slight difference to the term "blocked". > > The "block state" is a possible state of a task running in the deadline > scheduler. It means that a task voluntarily left the processor, not > by calling sched_yield(), but by blocking (or sleeping) waiting another > event. > > This state is described in the Figure 2 of the article "Deadline > scheduling in the Linux kernel", available at: > http://onlinelibrary.wiley.com/doi/10.1002/spe.2335/abstract Bah, confusing terminology. > > The block state affects the replenishment of the task, and that is why > it is different of both yeild and throttle. If the task blocks and is > awakened prior to the deadline, the task's runtime will not be > replenished. On the other hand it will. For example: > > Blocking, and then waking up after the deadline: > b-5152 [007] d..3 3983.376428: sched_deadline_replenish: > comm=b pid=5152 now=3983.376425148 deadline=3983.406425148 runtime=10000000 > b-5152 [007] d..3 3983.376515: sched_deadline_block: > now=3983.376511101 deadline=3983.406425148 remaining_runtime=9909566 > b-5152 [007] d..3 3983.376529: sched_switch: prev_comm=b > prev_pid=5152 prev_prio=-1 prev_state=S ==> next_comm=swapper/7 next_pid=0 > next_prio=120 > > <idle>-0 [007] d.h4 3983.476592: sched_deadline_replenish: > comm=b pid=5152 now=3983.476589573 deadline=3983.506589573 runtime=10000000 > <idle>-0 [007] dNh4 3983.476596: sched_wakeup: comm=b pid=5152 > prio=-1 target_cpu=007 > <idle>-0 [007] d..3 3983.476648: sched_switch: > prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=b > next_pid=5152 next_prio=-1 > b-5152 [007] d..3 3983.476660: sched_deadline_block: > now=3983.476656613 deadline=3983.506589573 remaining_runtime=9932960 > b-5152 [007] d..3 3983.476663: sched_switch: prev_comm=b > prev_pid=5152 prev_prio=-1 prev_state=S ==> next_comm=swapper/7 next_pid=0 > next_prio=120 > > > Blocking, and then waking up before the deadline: > b-5139 [007] d..3 3964.148290: sched_deadline_replenish: > comm=b pid=5139 now=3964.148285227 deadline=3964.178285227 runtime=10000000 > b-5139 [007] d..3 3964.148396: sched_deadline_block: > now=3964.148385308 deadline=3964.178285227 remaining_runtime=9895243 > b-5139 [007] d..3 3964.148400: sched_switch: prev_comm=b > prev_pid=5139 prev_prio=-1 prev_state=S ==> next_comm=swapper/7 next_pid=0 > next_prio=120 > > <idle>-0 [007] dNh5 3964.148411: sched_wakeup: comm=b pid=5139 > prio=-1 target_cpu=007 > <idle>-0 [007] d..3 3964.148419: sched_switch: > prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=b > next_pid=5139 next_prio=-1 > b-5139 [007] d..3 3964.148427: sched_deadline_block: > now=3964.148426022 deadline=3964.178285227 remaining_runtime=9878164 > b-5139 [007] d..3 3964.148429: sched_switch: prev_comm=b > prev_pid=5139 prev_prio=-1 prev_state=S ==> next_comm=swapper/7 next_pid=0 > next_prio=120 > I still fail to see the usefulness of the block tracepoint. I could imagine that if we add the dynamic part of the sched_switch tracepoint to include deadline and runtime, we would get the same information. -- Steve
