Re: NOHZ: local_softirq_pending - More info without need for specific code.

[Iratxo Pichel Ortiz <ipichel@albentia.com>]

Thomas,

Iratxo Pichel Ortiz wrote:
>>>  2.6.29-rt16, right ?
>>>       
>> I have also tried rt18, but as I had thought seeing change-logs, the
>> behavior is exactly the same.
>>     
You were right here :) It was 29.
>> Do you know what could be causing this issue. I have managed to repeat this
>> traces (NOHZ...) without using my code, using a workqueue and in the work
>> just by doing something like:
>>
>> work_func() {
>>   mdelay(10);
>>   msleep(10);
>>
>>  queue_work(myqueue, mywork);
>> }
>>
>> And then by heavy loading the box from the outside.
>>     
I have written a very small module that causes the 
"local_softirq_pending" under not some load. Please find code at the end 
of this email. Here is pasted some traces of dmesg (I have increased the 
ratelimit of the "NOHZ: local..." trace to 250.

The only strange thing here is that I am calling "set_workqueue_prio" (I 
have hacked source to export this symbol), and I am starting to think 
that this could not be a good idea. Any hints about this?

[  648.954000] NOHZ: local_softirq_pending 
0e                                                                                                                    

[  648.955000] NOHZ: local_softirq_pending 
0e                                                                                                                    

[  648.956000] NOHZ: local_softirq_pending 
0e                                                                                                                    

   
>>> Does it work when you disable CONFIG_NOHZ ?
>>>       
Still pending to test.
>> I will try this and let the list know.
>>     
>>> Thanks,
>>>
>>>        tglx
>>>       
#include <linux/module.h>
#include <linux/workqueue.h>
#include <linux/sched.h>
#include <linux/delay.h>

#define LATENCY_PRIO        98

static struct workqueue_struct* wq;
static struct work_struct        w;

void LatencyzerWork(struct work_struct* work)
{
    static int count;

    /* Busy and normal waiting */
    mdelay(10);
    msleep(1);

    /* Requeue work */
    if(count++ < 400000)
        queue_work(wq, &w);
    else
        printk("LAT: Count reached %d, stopped latencying\n", count);
}

int __init LatencyzerInit(void)
{
    /* Prepare workqueue */
    printk("LAT: Initializing latencyzer\n");
    if(!(wq = create_singlethread_workqueue("LATENCY"))) {
        printk("LAT: Error creating task\n");
        return -1;
    }

    /* Change workqueue prio */
    set_workqueue_prio(wq, SCHED_FIFO, LATENCY_PRIO, 1);
    printk("LAT: Task prio set to %u\n", LATENCY_PRIO);

    /* Run first iteration */
    INIT_WORK(&w, LatencyzerWork);
    queue_work(wq, &w);
    return 0;
}

void __exit LatencyzerExit(void)
{
    printk("Latencyzer exiting...\n");

    /* Done here */
    cancel_work_sync(&w);
    destroy_workqueue(wq);

    return;
}

module_init(LatencyzerInit);
module_exit(LatencyzerExit);
MODULE_LICENSE("GPL");

-- 
Iratxo Pichel Ortiz
Software Development Manager

Albentia Systems S.A.
http://www.albentia.com

Tel: +34 914400567
Cel: +34 663808405
Fax: +34 914400569

C\Margarita Salas 22
Parque Tecnológico de Leganés
Leganés (28918)
Madrid
Spain

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