Problem with wake_up using real-time scheduling

Problem with wake_up using real-time scheduling

[Zoltan Bus]

Hello,

I have a problem on kernel 2.6.26.3. I have a real-time task which
uses the select system call to poll my audio driver. The sleeping task
is waken up by wake_up() from an interrupt handler.
The problem is, that the wake_up() function  sometimes does not wake
up the task if real-time priority is used.

The try_to_wake_up() returns from the out_running section, because of the check

      if (p->se.on_rq)
              goto out_running;

There are no other tasks running when the poll function is called.

Is this a known problem? Is it fixed somehow in newer versions?
Unfortunately I do not have the possibility to change the newest kernel version.
I am a newbie at linux, thank you very much for your help.

Zoltan

Re: Problem with wake_up using real-time scheduling

[Robert Hancock]

On 06/30/2009 02:44 AM, Zoltan Bus wrote:
> Hello,
>
> I have a problem on kernel 2.6.26.3. I have a real-time task which
> uses the select system call to poll my audio driver. The sleeping task
> is waken up by wake_up() from an interrupt handler.
> The problem is, that the wake_up() function  sometimes does not wake
> up the task if real-time priority is used.
>
> The try_to_wake_up() returns from the out_running section, because of the check
>
>        if (p->se.on_rq)
>                goto out_running;
>
> There are no other tasks running when the poll function is called.
>
> Is this a known problem? Is it fixed somehow in newer versions?
> Unfortunately I do not have the possibility to change the newest kernel version.
> I am a newbie at linux, thank you very much for your help.

Most likely there is something you're doing wrong in your driver, we 
would have to see the source code to give many useful suggestions..

Re: Problem with wake_up using real-time scheduling

[Gregory Haskins]

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Zoltan Bus wrote:
> Hello,
>
> I have a problem on kernel 2.6.26.3. I have a real-time task which
> uses the select system call to poll my audio driver. The sleeping task
> is waken up by wake_up() from an interrupt handler.
> The problem is, that the wake_up() function  sometimes does not wake
> up the task if real-time priority is used.
>
> The try_to_wake_up() returns from the out_running section, because of the check
>
>       if (p->se.on_rq)
>               goto out_running;
>
> There are no other tasks running when the poll function is called.
>
> Is this a known problem? Is it fixed somehow in newer versions?
> Unfortunately I do not have the possibility to change the newest kernel version.
> I am a newbie at linux, thank you very much for your help.
>
>   

That *should* work fine.  Can you post your code?

Regards,
-Greg


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