Re: I/O operations priority in RTOS

[Jan Kiszka <jan.kiszka@web.de>]

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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. Useful for exclusively assigning virtual PCI functions of
network adapters etc. to user space stacks or hypervisors like QEMU/KVM
(for device pass-through). But it's not mainline yet. And it obviously
requires an IOMMU.

But the key point remains: "exclusively". Anything else cannot be
modeled efficiently via UIO or VFIO.

Jan


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