Re: I/O operations priority in RTOS

[Armin Steinhoff <armin@steinhoff.de>]

Jan Kiszka wrote:
> On 2011-06-05 10:46, Armin Steinhoff wrote:
>> Nicholas Mc Guire wrote:
>>> On Sat, 04 Jun 2011, Monica Puig-Pey wrote:
>>>
>>>> Hello,
>>>> I'm studying how to develop drivers in a real time OS and how do they
>>>> work. I'm using  Ubuntu 10.04 with the 2.6.31-11-rt patch installed.
>>>> I would like to know the priority when executing open(), read(), write()
>>>> and close() operations.
>>>> In my example the thread which is using the driver runs with 10 RTPRIO,
>>>> but I don't know what happens in kernel context with the priority when
>>>> running the I/O operations.
>>>> Thank you for your help, I don't know where to learn about this.
>>>>
>>> []
>>> Also when using bottom half mechanisms you need to take into account the
>>> priority of the kernel thread that manages the defered work items, so
>>> rt-drivers may have a different structure than normal drivers.
>> That's the reason why I prefer UIO based user space drivers !
> ...which are forced to use threaded IRQs over -rt as well.

What's wrong with that approach? You have an ISR in the kernel module 
and an interrupt thread at user space.
Seem OK for me since a long time with QNX :)
> Taking threaded IRQs out of the picture, bottom-half mechanisms usually
> come into play when dispatch workload that cannot be assigned to a
> specific user context is significant. But then UIO is the wrong approach
> anyway as it doesn't match well the requirements of multi-user device
> interfaces.
   Support of multi-user device interfaces at user space is just a 
design issue ... I use this concept since a long time with QNX :)

--Armin



> Jan
>