linux-kernel - Re: Changing Kernel thread priorities

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Message-ID: <4DEDE411.6010807@unican.es>
Date:	Tue, 7 Jun 2011 10:40:49 +0200
From:	Monica Puig-Pey <puigpeym@...can.es>
To:	<markh@...pro.net>
CC:	Rolando Martins <rolando.martins@...il.com>,
	<linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: Changing Kernel thread priorities

El 06/06/11 18:49, Mark Hounschell escribió:
> On 06/06/2011 07:58 AM, Monica Puig-Pey wrote:
>> El 06/06/11 13:54, Rolando Martins escribió:
>>> Hi,
>>> I use the following:
>>>
>>> PIDs=$(ps -eLo pid,cls,rtprio,pri,nice,cmd | grep -i "irq" | awk '{
>>> print $1; }' | xargs echo)
>>> for i in $PIDs
>>> do
>>> ret=$(chrt -f -p 99 $i)
>>> done
>>>
>>> This will change the kernel thread associated with an irq handler to
>>> RT FIFO prio 99.
>>> Just change the script to your specific interrupt.
>>>
>>> Hope it helps,
>>> Rolando
>>>
>>> On Mon, Jun 6, 2011 at 12:47 PM, Monica Puig-Pey<puigpeym@...can.es>
>>> wrote:
>>>> I am writing a driver which has one kernel thread associated with it.
>>>> I want to change the priority of this thread, so that I can specify the
>>>> order in which it is scheduled following an interrupt.
>>>> I'm using:
>>>>
>>>> sched_setscheduler(struct task_struct *, int, struct sched_param *);
>>>>
>>>> but it doesn't work. I tried to change the priority from the
>>>> init_module,
>>>> and also from the Kernel Thread, but there is no way.
>>>>
>>>> Kernel version is 2.6.31-11-rt
>>>>
>>>> What do I call to change a kernel thread priority?
>>>>
>>>> Thanks you very much
>>>>
>>>> Mónica
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe
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>>>>
>>
>> I need to change the priority from inside the driver, when creating the
>> kernel thread.
>> Your script is useful but it is done in user context,
>> Any other help please?
>
> What I do is record the PID of the thread in the driver, then create an
> IOCTL for your driver that user land can call that either returns the
> PID so you can do it in user land, or cause the IOCTL code to do it in
> the driver.
>
> The same can be done with the affinity of the IRQ if you record the IRQ
> number.
>
> Mark
> --
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> linux-rt-users" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html

But I don't have de PID of my Kthread, I only have the task_struc * that 
gives me the function:

  struct task_struct *kthread_create(int (*threadfn)(void *data),
                    void *data,
                    const char namefmt[], ...)

How could I get the PID, and which function should I use in the IOCTL 
(kernel context) for changing its priority?

Thank you so much for your help

Mónica
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