doubt on schedule_work() - work task getting scheduled lately

[Mulyadi Santosa]

On Fri, Jul 29, 2016 at 5:32 PM, Muni Sekhar <munisekharrms at gmail.com>
wrote:

> Hi All,
>
> I have a doubt regarding the workqueue scheduling.
>
> I am using the workqueue for processing the Rx Interrupt data. I am
> calling schedule_work() on receiving the Rx interrupt from hardware.
>
> I calculated the time between calling the schedule_work() and
> workqueue task actually getting executed, Here I see many cases of
> less than 100 us(It is fairly good).
>
> But sometimes I see 10’s of ms and a lot in the 100’s of ms. I have
> seen over 0.5 secs too. I would like to know why does sometimes kernel
> takes longer time(in milli seconds) to schedule it? Is there any way
> to reduce this time gap?
>
>
> My code:
>
> static void my_workqueuetask(struct work_struct *work)
> {
>     printk("In %s() \n",__func__);
>
>     mutex_lock(&bh_mutex);
>
>     //Do something here
>
>     mutex_unlock(&bh_mutex);
> }
>
>
> static irqreturn_t my_irq_handler(int irq, void *dev)
> {
>         ……;
>
>         if(Rx Interrupt)
>              schedule_work(&rx_work);
>
> return IRQ_HANDLED;
> }
>
> --
> Thanks,
> Sekhar
>
>
Hi Sekhar

In general, in non real time kernel, there is no way you can make sure your
work will be scheduled after N seconds.

Have you done simple statistic calculation how much % it is slower than 100
us, and how much % it is faster than 100 us?

IMHO, if slower % is lower than 1% of overall sample, I think it is still
acceptable, but this is up to your judgement

BTW, like other said too, that mutex_lock, have you also measured how long,
by average, the lock is taken?

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com
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