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. 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. Jan
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