Re: rt20 scheduling latency testcase and failure data

From: Ingo Molnar
Date: Thu May 18 2006 - 07:24:11 EST

* Darren Hart <dvhltc@xxxxxxxxxx> wrote:

> yet to see a missed period with the version of the program. While
> getting to this point, I did see some things that concerned me:
> sched_la-4856 3D... 4083us!: math_state_restore (device_not_available)
> sched_la-4856 3D... 16033us : smp_apic_timer_interrupt (4b3b98e8 0 0)
> Am I reading that right? 12ms to complete math_state_restore()? What
> does "device_not_available" mean here?

no - the kernel returned to userspace after doing the
math_state_restore, and the next thing you saw is the timer IRQ. The
tracer traces function entries, but not function exits.

> Here are some other similar traces:
> sched_la-5008 2D... 4104us!: math_state_restore (device_not_available)
> sched_la-5008 2.... 4992us > sys_clock_gettime (00000001 b7fc8378 0000007b)

same here: we returned to userspace after FPU restore, and the next
thing was a sys_clock_gettime() syscall ~800 usecs later.

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