Re:[PATCH] sched/rt: Decrease number of calls of push_rt_task() in push_rt_tasks()

Re:[PATCH] sched/rt: Decrease number of calls of push_rt_task() in push_rt_tasks()

[Kirill Tkhai]

> On 2013/2/5 15:22, Kirill Tkhai wrote:
> 
>>> Suppose we have a large number of cpus(say 4096), with the last one running
>>> a low-priority task on it. Is it possible with this patch we will never reach
>>> the last cpu in case that previous cpu has complete the pulled task?
>>
>> Yes. But this patch is about several pushable tasks on the same cpu.
>>
>> Kirill
> 
> Maybe I haven't make myself understood, but in that case, there will be a higher-priority
> task in the runqueue of the pushing cpu, and a lower-priority task running in the last cpu
> which could not be preempt by push_rt_task(), I don't think it's acceptable.

Sure, I tried to prevent the fact of call of this function with locks of spinlocks etc. It may
be useful on system like 2 CPU, but it's not necessary for large systems. I'm not persist in this.

Kirill

> 
> Hans
> 
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Re:[PATCH] sched/rt: Decrease number of calls of push_rt_task() in push_rt_tasks()

[Kirill Tkhai]

> On 2013/2/1 5:57, Kirill Tkhai wrote:
> 
>> 31.01.2013, 20:08, "Steven Rostedt" <rostedt@goodmis.org>:
>>
>>> On Mon, 2013-01-28 at 03:46 +0400, Kirill Tkhai wrote:
>>>
>>>> The patch aims to decrease the number of calls of push_rt_task()
>>>> in push_rt_tasks().
>>>>
>>>> It's not necessary to push more than 'num_online_cpus() - 1' tasks.
>>>> If just pushed task doesn't leave its new CPU during our local call
>>>> of push_rt_tasks() than we won't push another task to the CPU.
>>>> If it leave or change priority than it will pull new task by itself.
>>>
>>> I'm curious. Have you hit situations where this was an issue? Or was
>>> this just discovered by code review?
>>
>> No, I did't hit this situation. It's impossible to hook every situation.
>>
>> Thanks for your explanation.
>>
>> Kirill
> 
> Suppose we have a large number of cpus(say 4096), with the last one running
> a low-priority task on it. Is it possible with this patch we will never reach
> the last cpu in case that previous cpu has complete the pulled task?

Yes. But this patch is about several pushable tasks on the same cpu.

Kirill

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