Messages in this thread | | | Date | Mon, 29 Nov 2004 16:56:42 +0100 | From | Ingo Molnar <> | Subject | Re: Priority Inheritance Test (Real-Time Preemption) |
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* Esben Nielsen <simlo@phys.au.dk> wrote:
> On Mon, 29 Nov 2004, Ingo Molnar wrote: > > > [...] > > To give you an extreme example: you cannot run OpenOffice.org with > > SCHED_FIFO prio 99 and expect it to have any sane deterministic latency > > bounds. The simpler the app, the easier it is to control latencies. > > No, but I want to have my RT-subsystem to be not affected even if the > users choose to run 1000 soffice.bin at SCHED_NORMAL!! [...]
that is still the case, as long as it doesnt 'interact' with soffice.bin. Note that the same qualification holds for every hard-RT OS as well, with varying levels of 'interaction'. Interaction depends on what kind of synchronization the hard-RT task does, and depends on how the kernel itself implements various kernel features.
> [...] The problem is that a raw spinlock is used to lock for a > iteration over a list which can be O(number of waiters * locking > depth) long. As long as we are in the kernel both is "controlled", > i.e. one can see the worst-case number in stress test and know it > can't get worse. *
which list do you mean? Note that the pi_list depends on the number of _RT-tasks_, not on the number of SCHED_NORMAL tasks. So you can create an arbitrary number of SCHED_NORMAL tasks, they wont impact the overhead of mutexes!
i very intentionally made it independent of nr-of-non-RT-tasks.
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