Hi everybody,
I have a question concerning maximum performance. In a simulation
system that is realized using LXRT userspace and that runs
periodically (let's say every a milliseconds), it might be useful to
have the full network driver realized in user space as well. I think
that each change between user and kernel space is fairly expensive. Thus, when I do not want to use interrupts, it could be a really fast
solution to realize the network driver and all layers above (rtnet)
as pure user space (LXRT) programs. The questions: Is is possible, to
get a network driver running without interrupts? In this scenario,
the driver could be polled every simulation step which is faster than
switching completely to kernel mode.
What do you think about this - what about the performance gain?
Any comments on this are welcome!
Converting the devices drivers so that polling is used should be possible. Take a look at modern drivers supporting the NAPI. This interface is intended to reduce the CPU load caused by a very high number of interrupts, e.g. caused by GBit Ethernet.
But there are other issue you will face when moving RTnet to user space: low level synchronisation (spin and IRQ locks) or the usage of various kernel functions (PCI, DMA, etc.). I'm not sure at the moment if there are solutions available worth the effort. And if this will be faster than calling standard RTnet from user space - I don't think so.
Jan
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