linux-kernel - Re: How can I migrate a currently running task?

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Date:	Sat, 28 Jun 2008 12:05:21 +0800
From:	xialiang <xiaiaxaxi@...u.edu.cn>
To:	Robin Holt <holt@....com>
Cc:	Bart Van Assche <bart.vanassche@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: How can I migrate a currently running task?

Quoting Robin Holt <holt@....com>:

> On Fri, Jun 27, 2008 at 09:38:05PM +0800, xialiang wrote:
>> Quoting Bart Van Assche <bart.vanassche@...il.com>:
>>
>>> On Fri, Jun 27, 2008 at 3:17 PM, 夏亮 <xiaiaxaxi@...u.edu.cn> wrote:
>>>> I am working on Intel Duo Core with Linux OS 2.6.21, and I'd like to
>>>> migrate task from one cpu to another cpu.
>>>> In SMP systems, load_balance() function uses move_tasks() to move  
>>>>  processes
>>>> from source runqueue to local runqueue, but it does not move a currently
>>>> running task. If I want to migrate a currently running task from source
>>>> runqueue to local runqueue, how can I do? Any suggestion is preferred.
>>>
>>> Are you familiar with the glibc pthread_setaffinity_np() function
>>> and/or the sched_setaffinity() system call ?
>>>
>>> Bart.
>>>
>>
>> Yes. I know sched_setaffinity(), it sets cpu_mask of a task. I want to
>> use it in a timer interrupt( scheduler_tick() ), can I?
>
> Don't use it from a timer handler.  You can use migrate_task() to move the
> task, but your email from a couple days ago said you wanted to move the
> task at the head of the runqueue due to cpu heat or something like that.
> That is a very imprecise way to move the task as any unfortunate task
> that happens to be running when the timer tick occurs could get migrated,
> not the one generating the work.
>
> I think you really want to look at the other areas of the kernel which do
> stuff like throttling the cpu.  Just moving a task off the cpu does not
> prevent it from being used for another compute intesive load.  You could
> take the cpu offline.  I guess to do that, I would use schedule_work()
> or kthread_create() to get out of the timer context and into a regular
> thread context then take the cpu offline from there.
>
> Good Luck,
> Robin
>

       I would move a task at the head of the runqueue, but I already  
know which task creates the heat. I get the profile of tasks  
beforehand. So if I find the temperature of a cpu is much higher than  
that of the other, and coincidentally the currently running task of  
the cpu is what I want to migrate. Can I migrate it in the  
scheduler_tick()? Or where should I put the migration code? Thanks!

Best regards,
Liang

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