Re: Changing Kernel thread priorities

From: Mark Hounschell
Date: Tue Jun 07 2011 - 14:55:25 EST

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
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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
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