Re: How can I migrate a currently running task?

[xialiang]

Quoting Robin Holt <holt@xxxxxxx>:

> On Fri, Jun 27, 2008 at 09:38:05PM +0800, xialiang wrote:
> > Quoting Bart Van Assche <bart.vanassche@xxxxxxxxx>:
> >
> > > On Fri, Jun 27, 2008 at 3:17 PM, 夏亮 <xiaiaxaxi@xxxxxxxxxxx> 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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