On 12/11/2012 12:23 PM, Preeti U Murthy wrote:
> Hi Alex,
>
> On 12/10/2012 01:52 PM, Alex Shi wrote:
>> It is impossible to miss a task allowed cpu in a eligible group.
>
> The one thing I am concerned with here is if there is a possibility of
> the task changing its tsk_cpus_allowed() while this code is running.
>
> i.e find_idlest_group() finds an idle group,then the tsk_cpus_allowed()
> for the task changes,perhaps by the user himself,which might not include
> the cpus in the idle group.After this find_idlest_cpu() is called.I mean
> a race condition in short.Then we might not have an eligible cpu in that
> group right?
your worry make sense, but the code handle the situation, in
select_task_rq(), it will check the cpu allowed again. if the answer is
no, it will fallback to old cpu.
>
>> And since find_idlest_group only return a different group which
>> excludes old cpu, it's also imporissible to find a new cpu same as old
>> cpu.
>
> This I agree with.
>
>> Signed-off-by: Alex Shi <alex....@intel.com>
>> ---
>> kernel/sched/fair.c | 5 -----
>> 1 files changed, 0 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 59e072b..df99456 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3150,11 +3150,6 @@ select_task_rq_fair(struct task_struct *p, int
>> sd_flag, int wake_flags)
>> }
>>
>> new_cpu = find_idlest_cpu(group, p, cpu);
>> - if (new_cpu == -1 || new_cpu == cpu) {
>> - /* Now try balancing at a lower domain level of cpu */
>> - sd = sd->child;
>> - continue;
>> - }
>>
>> /* Now try balancing at a lower domain level of new_cpu */
>> cpu = new_cpu;
>>
> Regards
> Preeti U Murthy
>
--
Thanks
Alex
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