[Crash-utility] [PATCH] Fix bugs in runq

[Dave Anderson]

----- Original Message -----

> Hmm, may be confusing here...
> 
> >> crash> runq
> >> CPU 0 RUNQUEUE: ffff880028216680
> >>   CURRENT: PID: 5125   TASK: ffff88010799d540  COMMAND: "sh"
> >>   RT PRIO_ARRAY: ffff880028216808
> >>      [  0] PID: 5136   TASK: ffff8801153cc040  COMMAND: "rtloop99"
> >>            CHILD RT PRIO_ARRAY: ffff88013b050000
> >>               [  0] PID: 5133   TASK: ffff88010799c080  COMMAND: "rtloop99"
> >>               [  1] PID: 5131   TASK: ffff880037922aa0  COMMAND: "rtloop98"
> >>               [ 98] PID: 5128   TASK: ffff88011bd87540  COMMAND: "rtloop1"
> >>                     PID: 5130   TASK: ffff8801396e7500  COMMAND: "rtloop1"
> >>                     PID: 5129   TASK: ffff88011bf5a080  COMMAND: "rtloop1"
> >>            PID: 6      TASK: ffff88013d7c6080  COMMAND: "watchdog/0"
> >>            PID: 3      TASK: ffff88013d7ba040  COMMAND: "migration/0"
> >>      [  1] PID: 5134   TASK: ffff8801153cd500  COMMAND: "rtloop98"
> >>            PID: 5135   TASK: ffff8801153ccaa0  COMMAND: "rtloop98"
> >> ...
> > 
> > whereas on cpu 1, the "CHILD RT PRIO ARRAY" line is on the same
> > line as
> > priority 54:
> > 
> >> CPU 1 RUNQUEUE: ffff880028296680
> >>   CURRENT: PID: 5086   TASK: ffff88006eecc040  COMMAND: "bash"
> >>   RT PRIO_ARRAY: ffff880028296808
> >>      [  0] PID: 5137   TASK: ffff880107b35540  COMMAND: "rtloop99"
> >>            PID: 10     TASK: ffff88013cc2cae0  COMMAND: "watchdog/1"
> >>            PID: 2852   TASK: ffff88013bd5aae0  COMMAND: "rtkit-daemon"
> >>      [ 54] CHILD RT PRIO_ARRAY: ffff880138978000 
> >>               [ 54] PID: 5132   TASK: ffff88006eecd500  COMMAND: "rtloop45"
> >>   CFS RB_ROOT: ffff880028296718
> > 
> > What is it a "child" of?  Or maybe "CHILD" the wrong terminology
> > here?
> 
> 
> Now, the scheduler is not limited to schedule processes, but can also
> work with larger entities. This allows for implementing group
> scheduling.
> 
> So for every RT PRIO_ARRAY, each linked list for each priority has
> its element embedded in a structure "sched_entity". This "sched_entity"
> could represent two things: a process or a child rt runqueue.
> 
> for example, in cpu0, array[0] has four linked elements:
>     1. task 5136
>     2. a child rt rq
>     3. task 6
>     4. task 3
> and the child rt rq has its own runqueue array with 5 tasks in it:
> task 5133 with a priority of 0, task 5131 with a priority of 1, and the
> last three tasks -- 5128, 5230, 5129 with a priority of 98.

Right, I understand.  What I don't understand is the use of the "child"
terminology.  If CONFIG_RT_GROUP_SCHED is configured, then the sched_rt_entity
may reference a "group" run queue.  To me, it doesn't make sense to use
the term "CHILD RT PRIO_ARRAY" in the header.  Wouldn't it make more sense to
call it a "GROUP RT PRIO_ARRAY"?  Like this: 

crash> runq
CPU 0 RUNQUEUE: ffff880028216680
  CURRENT: PID: 5125   TASK: ffff88010799d540  COMMAND: "sh"
  RT PRIO_ARRAY: ffff880028216808
     [  0] PID: 5136   TASK: ffff8801153cc040  COMMAND: "rtloop99"
           GROUP RT PRIO_ARRAY: ffff88013b050000
             [  0] PID: 5133   TASK: ffff88010799c080  COMMAND: "rtloop99"
             [  1] PID: 5131   TASK: ffff880037922aa0  COMMAND: "rtloop98"
             [ 98] PID: 5128   TASK: ffff88011bd87540  COMMAND: "rtloop1"
                   PID: 5130   TASK: ffff8801396e7500  COMMAND: "rtloop1"
                   PID: 5129   TASK: ffff88011bf5a080  COMMAND: "rtloop1"
          PID: 6      TASK: ffff88013d7c6080  COMMAND: "watchdog/0"
          PID: 3      TASK: ffff88013d7ba040  COMMAND: "migration/0"
    [  1] PID: 5134   TASK: ffff8801153cd500  COMMAND: "rtloop98"
          PID: 5135   TASK: ffff8801153ccaa0  COMMAND: "rtloop98"
    ...


CPU 1 RUNQUEUE: ffff880028296680
  CURRENT: PID: 5086   TASK: ffff88006eecc040  COMMAND: "bash"
  RT PRIO_ARRAY: ffff880028296808
     [  0] PID: 5137   TASK: ffff880107b35540  COMMAND: "rtloop99"
           PID: 10     TASK: ffff88013cc2cae0  COMMAND: "watchdog/1"
           PID: 2852   TASK: ffff88013bd5aae0  COMMAND: "rtkit-daemon"
     [ 54] GROUP RT PRIO_ARRAY: ffff880138978000 
             [ 54] PID: 5132   TASK: ffff88006eecd500  COMMAND: "rtloop45"
  CFS RB_ROOT: ffff880028296718
  ... 

Thanks,
  Dave