Re: [PATCH] runq: search current task's runqueue explicitly

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From: Dave Anderson <anderson@xxxxxxxxxx>
Subject: Re:  [PATCH] runq: search current task's runqueue explicitly
Date: Thu, 05 Jan 2012 15:32:12 -0500 (EST)

> 
> 
> ----- Original Message -----
>> Currently, runq sub-command doesn't consider CFS runqueue's current
>> task removed from CFS runqueue. Due to this, the remaining CFS
>> runqueus that follow the current task's is not displayed. This patch
>> fixes this by making runq sub-command search current task's runqueue
>> explicitly.
>> 
>> Note that CFS runqueue exists for each task group, and so does CFS
>> runqueue's current task, and the above search needs to be done
>> recursively.
>> 
>> Test
>> ====
>> 
>> On vmcore I made 7 task groups:
>> 
>>   root group --- A --- AA --- AAA
>>                     +      +- AAB
>>                     |
>>                     +- AB --- ABA
>>                            +- ABB
>> 
>> and then I ran three CPU bound tasks, which is exactly the same as
>> 
>>   int main(void) { for (;;) continue; return 0; }
>> 
>> for each task group, including root group; so total 24 tasks. For
>> readability, I annotated each task name with its belonging group name.
>> For example, loop.ABA belongs to task group ABA.
>> 
>> Look at CPU0 collumn below. [before] lacks 8 tasks and [after]
>> successfully shows all tasks on the runqueue, which is identical to
>> the result of [sched debug] that is expected to ouput correct result.
>> 
>> I'll send this vmcore later.
>> 
>> [before]
>> 
>> crash> runq | cat
>> CPU 0 RUNQUEUE: ffff88000a215f80
>>   CURRENT: PID: 28263  TASK: ffff880037aaa040  COMMAND: "loop.ABA"
>>   RT PRIO_ARRAY: ffff88000a216098
>>      [no tasks queued]
>>   CFS RB_ROOT: ffff88000a216010
>>      [120] PID: 28262  TASK: ffff880037cc40c0  COMMAND: "loop.ABA"
>> 
>> <cut>
>> 
>> [after]
>> 
>> crash_fix> runq
>> CPU 0 RUNQUEUE: ffff88000a215f80
>>   CURRENT: PID: 28263  TASK: ffff880037aaa040  COMMAND: "loop.ABA"
>>   RT PRIO_ARRAY: ffff88000a216098
>>      [no tasks queued]
>>   CFS RB_ROOT: ffff88000a216010
>>      [120] PID: 28262  TASK: ffff880037cc40c0  COMMAND: "loop.ABA"
>>      [120] PID: 28271  TASK: ffff8800787a8b40  COMMAND: "loop.ABB"
>>      [120] PID: 28272  TASK: ffff880037afd580  COMMAND: "loop.ABB"
>>      [120] PID: 28245  TASK: ffff8800785e8b00  COMMAND: "loop.AB"
>>      [120] PID: 28246  TASK: ffff880078628ac0  COMMAND: "loop.AB"
>>      [120] PID: 28241  TASK: ffff880078616b40  COMMAND: "loop.AA"
>>      [120] PID: 28239  TASK: ffff8800785774c0  COMMAND: "loop.AA"
>>      [120] PID: 28240  TASK: ffff880078617580  COMMAND: "loop.AA"
>>      [120] PID: 28232  TASK: ffff880079b5d4c0  COMMAND: "loop.A"
>> <cut>
>> 
>> [sched debug]
>> 
>> crash> runq -d
>> CPU 0
>>      [120] PID: 28232  TASK: ffff880079b5d4c0  COMMAND: "loop.A"
>>      [120] PID: 28239  TASK: ffff8800785774c0  COMMAND: "loop.AA"
>>      [120] PID: 28240  TASK: ffff880078617580  COMMAND: "loop.AA"
>>      [120] PID: 28241  TASK: ffff880078616b40  COMMAND: "loop.AA"
>>      [120] PID: 28245  TASK: ffff8800785e8b00  COMMAND: "loop.AB"
>>      [120] PID: 28246  TASK: ffff880078628ac0  COMMAND: "loop.AB"
>>      [120] PID: 28262  TASK: ffff880037cc40c0  COMMAND: "loop.ABA"
>>      [120] PID: 28263  TASK: ffff880037aaa040  COMMAND: "loop.ABA"
>>      [120] PID: 28271  TASK: ffff8800787a8b40  COMMAND: "loop.ABB"
>>      [120] PID: 28272  TASK: ffff880037afd580  COMMAND: "loop.ABB"
>> <cut>
>> 
>> Diff stat
>> =========
>> 
>>  defs.h |    1 +
>>  task.c |   37 +++++++++++++++++--------------------
>>  2 files changed, 18 insertions(+), 20 deletions(-)
>> 
>> Thanks.
>> HATAYAMA, Daisuke
> 
> Hello Daisuke,
> 
> Good catch!  Plus your re-worked patch cleans things up nicely.
> 
> And "runq -d" paid off quickly, didn't it?  ;-)
> 
> One minor problem, while testing your patch on a variety of kernels,
> several "runq" commands failed because the test kernels were 
> not configured with CONFIG_FAIR_GROUP_SCHED:
>   
>   struct sched_entity {
>           struct load_weight      load;           /* for load-balancing */
>           struct rb_node          run_node;
>           struct list_head        group_node;
>           unsigned int            on_rq;
>   
>           u64                     exec_start;
>           u64                     sum_exec_runtime;
>           u64                     vruntime;
>           u64                     prev_sum_exec_runtime;
>   
>           u64                     nr_migrations;
>   
>   #ifdef CONFIG_SCHEDSTATS
>           struct sched_statistics statistics;
>   #endif
>   
>   #ifdef CONFIG_FAIR_GROUP_SCHED
>           struct sched_entity     *parent;
>           /* rq on which this entity is (to be) queued: */
>           struct cfs_rq           *cfs_rq;
>           /* rq "owned" by this entity/group: */
>           struct cfs_rq           *my_q;
>   #endif
>   };
>   
> so they failed like so:
>   
>   CPU 0 RUNQUEUE: ffffffff825f7520
>     CURRENT: PID: 3790   TASK: ffff88000c8f2cf0  COMMAND: "bash"
>     RT PRIO_ARRAY: ffffffff825f75e8
>        [no tasks queued]
>     CFS RB_ROOT: ffffffff825f75a0
>   runq: invalid structure member offset: sched_entity_my_q
>         FILE: task.c  LINE: 7035  FUNCTION: dump_tasks_in_cfs_rq()
>   
> where line 7035 is where the first possible recursion is done:
> 
>  7021 static int
>  7022 dump_tasks_in_cfs_rq(ulong cfs_rq)
>  7023 {
>  7024         struct task_context *tc;
>  7025         struct rb_root *root;
>  7026         struct rb_node *node;
>  7027         ulong my_q, leftmost, curr, curr_my_q;
>  7028         int total;
>  7029 
>  7030         total = 0;
>  7031 
>  7032         readmem(cfs_rq + OFFSET(cfs_rq_curr), KVADDR, &curr, sizeof(ulong),
>  7033                 "curr", FAULT_ON_ERROR);
>  7034         if (curr) {
>  7035                 readmem(curr + OFFSET(sched_entity_my_q), KVADDR, &curr_my_q,
>  7036                         sizeof(ulong), "curr->my_q", FAULT_ON_ERROR);
>  7037                 if (curr_my_q)
>  7038                         total += dump_tasks_in_cfs_rq(curr_my_q);
>  7039         }  
>  7040
>  7041         readmem(cfs_rq + OFFSET(cfs_rq_rb_leftmost), KVADDR, &leftmost,
>  7042                 sizeof(ulong), "rb_leftmost", FAULT_ON_ERROR);
>  7043         root = (struct rb_root *)(cfs_rq + OFFSET(cfs_rq_tasks_timeline));
>  7044 
>  7045         for (node = rb_first(root); leftmost && node; node = rb_next(node)) {
>  7046                 if (VALID_MEMBER(sched_entity_my_q)) {
>  7047                         readmem((ulong)node - OFFSET(sched_entity_run_node)
>  7048                                 + OFFSET(sched_entity_my_q), KVADDR, &my_q,
>  7049                                 sizeof(ulong), "my_q", FAULT_ON_ERROR);
>  7050                         if (my_q) {
>  7051                                 total += dump_tasks_in_cfs_rq(my_q);
>  7052                                 continue;
>  7053                         }
>  7054                 }
> 
> I fixed it by imposing a VALID_MEMBER(sched_entity_my_q) check, similar
> to what is done at the second recursive call at line 7046 above:
> 
>         if (VALID_MEMBER(sched_entity_my_q)) {
>                 readmem(cfs_rq + OFFSET(cfs_rq_curr), KVADDR, &curr,
>                         sizeof(ulong), "curr", FAULT_ON_ERROR);
>                 if (curr) {
>                         readmem(curr + OFFSET(sched_entity_my_q), KVADDR,
>                                 &curr_my_q, sizeof(ulong), "curr->my_q",
>                                 FAULT_ON_ERROR);
>                         if (curr_my_q)
>                                 total += dump_tasks_in_cfs_rq(curr_my_q);
>                 }
>         }
> 
> and that worked OK.
> 
> I also added "sched_entity_my_q" to dump_offset_table() for "help -o".
> 
> If you are OK with the changes above, the patch is queued for crash-6.0.3.
> 

I missed the case where fair scheduler is disabled.

I'm of course OK. Thanks for the fix.

Thanks.
HATAYAMA, Daisuke

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