Re: 4.9.6-rt4: big latency due to a kworker upon serial interrupts

[Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>]

On 2017-01-31 17:05:28 [+0100], thierry bultel wrote:
> Hi,
Hi,

…
> To reproduce this very easily, I generate interrupts by just keeping
> the return key pressed in the serial console.
> It it also reproducible, by performing a 'ping -f' from another machine.
> 
…

> #define MY_PRIORITY (49) /* we use 49 as the PRREMPT_RT use 50
>                                 as the priority of kernel tasklets
>                                 and interrupt handler by default */
> 
…
> 	param.sched_priority = MY_PRIORITY;
> 	if(sched_setscheduler(0, SCHED_FIFO, &param) == -1) {

If I read this right your application has a lower priority than the
threaded interrupt which means the interrupt will be preferred over the
application. This in turn means the your application won't wake up in
time if there is an interrupt pending. However the kworker should not
block the application.

Sebastian
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