Re: Changing Kernel thread priorities

[Mark Hounschell <markh@compro.net>]

On 06/07/2011 02:34 PM, Monica Puig-Pey wrote:
> El 07/06/11 11:46, Mark Hounschell escribió:
>> On 06/07/2011 05:14 AM, Mark Hounschell wrote:
>>> On 06/07/2011 04:40 AM, Monica Puig-Pey wrote:
>>>> 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
>>>>>>> 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
>>>>>>>>
>>>>>>>> --
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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
>>>>> --
>>>>> To unsubscribe from this list: send the line "unsubscribe
>>>>> linux-rt-users" in
>>>>> the body of a message to majordomo@vger.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?
>>>>
>>>
>>> The PID can be obtained from within the interrupt handler its self via
>>> current->pid.
>>> Obviously an interrupt has to occur first but after one interrupt you
>>> have it.
>>>
>>> Actually I had forgot how I handled this. Where I change the RT priority
>>> and cpu affinity is in what used to be called the Bottom Half and the
>>> IOCTL
>>> referred to above simply tells the BH to do it and with what values.
>>>
>>
>> In interrupt handler code snippet:
>>
>> struct task_struct *TSK;
>> struct sched_param PARAM = {.sched_priority = MAX_RT_PRIO };
>>
>> TSK = current;
>>
>> Code snippet from BH:
>>
>> if (((rtom_rtprio != 0) &&
>> (rtom_rtprio != PARAM.sched_priority)) ||
>> (my_rtom_rtprio[BOARD] != rtom_rtprio)) {
>>
>> PARAM.sched_priority = rtom_rtprio;
>> my_rtom_rtprio[COUNT] = rtom_rtprio;
>> sched_setscheduler(TSK, SCHED_FIFO, &PARAM);
>>
>> set_cpus_allowed(TSK, rtom_devices[BOARD].irq_cpu_mask);
>> rtom_devices[BOARD].irq_task_pid = TSK->pid;
>> }
>>
>> rtom_rtprio and irq_cpu_mask are set by userland via an IOCTL. An
>> interrupt must occur for this to happen and my BOARD never shares IRQs.
>>
>> Mark
>>
>
> Thanks, your idea seems to be very useful to me. I was doing it very
> similar, but I didn't use the "current" variable to know the task_struct *.
>
> I have tried your suggestion on an easy example, but it didn't work.
> Insmod returns through the kernel
>
> [11334.895499] kthread: Unknown symbol sched_setscheduler
>
> Code shown below:
>
> #include <linux/module.h>
> #include <linux/kernel.h>
> #include <linux/ioport.h>
>
> #include <linux/wait.h>
> #include <linux/kthread.h>
> #include <asm/io.h>
> #include <linux/sched.h>
>
>
> struct task_struct *ts;
>
> int thread(void *data)
> {
> struct task_struct *TSK;
> struct sched_param PARAM = {.sched_priority = MAX_RT_PRIO };
> TSK = current;
>
> PARAM.sched_priority = 50;
> sched_setscheduler(TSK, SCHED_FIFO, &PARAM); // <-- unknown symbol??
>
> while(1){
> printk("Hi I am kernel thread!\n");
> msleep(100);
> if (kthread_should_stop())
> break;
> }
> return 0;
> }
>
>
> int init_module(void)
> {
> printk(KERN_INFO "init_module() called\n");
> ts=kthread_run(thread,NULL,"kthread");
> return 0;
> }
>
> void cleanup_module(void)
> {
> printk(KERN_INFO "cleanup_module() called\n");
> kthread_stop(ts);
> }
> .
>

In kernel/sched.c

EXPORT_SYMBOL_GPL(sched_setscheduler);

If your driver is not GPL, you can't use it.

Mark