Messages in this thread | | | Date | Mon, 1 Nov 2004 19:43:04 +0100 | From | Ingo Molnar <> | Subject | Re: [Fwd: Re: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0.4] |
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* Lee Revell <rlrevell@joe-job.com> wrote:
> This was my conclusion as well. I have a patch sitting around to add > this to the emu10k1 ALSA driver, it's quite useful. It would be nice > if there were a facility in the kernel to easily identify missed > interrupts like this or (even better) unbalanced irq disable/enable - > AFAICT userspace alone cannot reliably distinguish lost interrupts > from scheduling problems (though you can get a lot of hints). Paul > mentioned trying to debug the unbalanced irq disable in his talk at > ZKM 2003, and said it's hard because the hardware will enable/disable > interrupts on its own and he could not identify all those places. > Ingo, is there an easy way to trace this like we do for unbalanced > preempt count?
i wrote a cli/sti latency tracer a couple of years ago so it's possible. Note that an irqs-off condition is near impossible to 'leak' into userspace code though, since the x86 iret path restores flags to the previous value. Worst-case the irqs-off condition may leak into kernelspace, and that can still cause bad effects. X startup/shutdown can disable interrupts for a long time, was that excluded from your testing?
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