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    SubjectRe: 2.6.16-rt10

    * Simon Derr <> wrote:

    > On Tue, 28 Mar 2006, Ingo Molnar wrote:
    > >
    > > * Simon Derr <> wrote:
    > >
    > > > On Mon, 27 Mar 2006, Ingo Molnar wrote:
    > > >
    > > > > i've released -rt10
    > > >
    > > > Is anyone working on a port of this patch to the IA64 architecture ?
    > >
    > > not that i know of. If someone wants to do that, take a look at the
    > > x86_64 changes (or ppc/mips/i386 changes) to get an idea. These are the
    > > rough steps needed:
    > > [snip]
    > Work in progress... (based on -rt11)
    > So far I have a kernel that almost boots, but not quite.
    > First issue: 'BUG: udev:45 task might have lost a preemption check!'
    > When looking at the code in preempt_enable_no_resched(), why is the
    > value of preempt_count() checked to be non-zero _after_ calling
    > dec_preempt_count() ?
    > I saw several posts on this list claiming that this message is
    > harmless, but I'd like to figure what's going on.

    the warning means that doing a preempt_enable_no_resched() while being
    in a preemptible section is most likely a bug, and that you could lose a
    need_resched() check. (and introduce a scheduling latency) What's the
    backtrace? This could be the sign of a not fully/correctly converted
    arch/*/kernel/process.c (but i'm only guessing here).

    > My boot process is stuck later when insmod loads the driver for the
    > MPT Fusion SCSI adapter. It's waiting for a second interrupt to
    > arrive, and that never happens.
    > I see that the -rt patch touches many drivers by changing calls to
    > local_irq_save (and friends), changing the type of the semaphores, but
    > the MPT driver makes no use of these.
    > Any ideas ?

    you should first check the PREEMPT_NONE kernel with PREEMPT_SOFTIRQS and
    PREEMPT_HARDIRQS enabled. I.e. first check whether IRQ threading works.
    Then enable all the other PREEMPT options one by one: PREEMPT_DESKTOP,
    PREEMPT_RCU, PREEMPT_BKL. Only when all these work switch to PREEMPT_RT.

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