Re: I/O operations priority in RTOS

[Armin Steinhoff <armin@steinhoff.de>]

Jan Kiszka wrote:
> On 2011-06-05 11:28, Nicholas Mc Guire wrote:
>> On Sun, 05 Jun 2011, 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 !
>>>
>> ...and how to resolve DMA ? if DMA were resolved cleanly I would agree.
> Regarding that limitation, there is some hope: "next-generation" UIO is
> called VFIO.

I found in a posting about VFIO that  " ioctls are used for all the 
basic interactions"  ... that means VFIO works with a lot of context 
switches.
That's not the case with UIO.  So why should VFIO be a mainline approach 
or next generation UIO at all?

--Armin