Did you tried ftrace? https://www.kernel.org/doc/Documentation/trace/ftrace.txt

I've been using this to measure some latencies. The problem here is
visualizing the output. If you need someting more elaborated than
simple prints with timestamps and delta calculations, then you should
try something more complex. If not you can enable FTRACE and generate
trace output with delta timestamps on it, event for interrupts :)

Best regards,

2016-08-01 7:32 GMT-03:00 Muni Sekhar [off-list ref]:

On Fri, Jul 29, 2016 at 9:05 PM, Daniel. [off-list ref] wrote:

quoted

Nice tool @Ricardo!

2016-07-29 10:48 GMT-03:00 Ricardo Ribalda Delgado [off-list ref]:

quoted

you can use http://lttng.org/ for analyzing this

Thanks Ricardo, I will use this.

quoted

quoted

Regards!

On Fri, Jul 29, 2016 at 12:44 PM, Pranay Srivastava [off-list ref] wrote:

quoted

On Fri, Jul 29, 2016 at 4:02 PM, Muni Sekhar [off-list ref] wrote:

quoted

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__);

You probably don't need this if it's just for your work_fn, yeah but
if there's race between this and something else...

quoted

    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);

Maybe system_wq has too much already on it's plate?
Have you tried the same with completion and a kthread? or
with your own workqueue, overkill but you can give it a shot.

I have not tried this. First I will analyze with lttng and then
attempts this. Does using our own workqueue reduces the latency?

quoted

quoted

quoted

quoted

return IRQ_HANDLED;
}

--
Thanks,
Sekhar

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Thanks,
Sekhar

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  Yoda Master