Re: [RFC PATCH 0/2] sched: simplify the select_task_rq_fair()

[Michael Wang <wangyun@linux.vnet.ibm.com>]

On 01/21/2013 05:09 PM, Mike Galbraith wrote:
> On Mon, 2013-01-21 at 15:45 +0800, Michael Wang wrote: 
>> On 01/21/2013 03:09 PM, Mike Galbraith wrote:
>>> On Mon, 2013-01-21 at 07:42 +0100, Mike Galbraith wrote: 
>>>> On Mon, 2013-01-21 at 13:07 +0800, Michael Wang wrote:
>>>
>>>>> May be we could try change this back to the old way later, after the aim
>>>>> 7 test on my server.
>>>>
>>>> Yeah, something funny is going on.
>>>
>>> Never entering balance path kills the collapse.  Asking wake_affine()
>>> wrt the pull as before, but allowing us to continue should no idle cpu
>>> be found, still collapsed.  So the source of funny behavior is indeed in
>>> balance_path.
>>
>> Below patch based on the patch set could help to avoid enter balance path
>> if affine_sd could be found, just like the old logical, would you like to
>> take a try and see whether it could help fix the collapse?
> 
> No, it does not.

Hmm...what have changed now compared to the old logical?

May be I missed some thing, well, I think I need to find a machine which
could reproduce the issue firstly.

Regards,
Michael Wang

> 
>>
>> Regards,
>> Michael Wang
>>
>> ---
>>  kernel/sched/fair.c |   14 ++++++++------
>>  1 files changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index d600708..4e95bb0 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3297,6 +3297,8 @@ next:
>>                         sg = sg->next;
>>                 } while (sg != sd->groups);
>>         }
>> +
>> +       return -1;
>>  done:
>>         return target;
>>  }
>> @@ -3349,7 +3351,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
>>                  * some cases.
>>                  */
>>                 new_cpu = select_idle_sibling(p, prev_cpu);
>> -               if (idle_cpu(new_cpu))
>> +               if (new_cpu != -1)
>>                         goto unlock;
>>
>>                 /*
>> @@ -3363,15 +3365,15 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
>>                         goto balance_path;
>>
>>                 new_cpu = select_idle_sibling(p, cpu);
>> -               if (!idle_cpu(new_cpu))
>> -                       goto balance_path;
>> -
>>                 /*
>>                  * Invoke wake_affine() finally since it is no doubt a
>>                  * performance killer.
>>                  */
>> -               if (wake_affine(sbm->affine_map[prev_cpu], p, sync))
>> -                       goto unlock;
>> +               if (new_cpu == -1 ||
>> +                       !wake_affine(sbm->affine_map[prev_cpu], p, sync))
>> +                       new_cpu = prev_cpu;
>> +
>> +               goto unlock;
>>         }
>>
>>  balance_path:
> 
> 
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