Matthew Fornero wrote:
> On Thu, Nov 6, 2008 at 8:51 AM, Gilles Chanteperdrix
> <[EMAIL PROTECTED]> wrote:
>> Matthew Fornero wrote:
>>> On Tue, Nov 4, 2008 at 2:21 PM, Gilles Chanteperdrix
>>> <[EMAIL PROTECTED]> wrote:
>>>> Matthew Fornero wrote:
>>>>> Hello,
>>>>>
>>>>> I have an application on x86 that uses an external event (either an
>>>>> interrupt or a DMA write to a specific memory location) to trigger code
>>>>> execution, and I believe the local timer interrupt is contributing a
>>>>> significant amount of jitter. This is a bit of a unique case where the
>>>>> only
>>>>> code that should be executing on that core is triggered by the event, so
>>>>> there is no need for anything timer based.
>>>>>
>>>>> I'm using a dual core processor with a quiet system, and have placed all
>>>>> of
>>>>> the "moveable" interrupts on CPU 0 (0-NR_IRQs using
>>>>> ipipe_set_irq_affinity).
>>>>> Looking at /proc/xenomai/irq and /proc/interrupts shows only the local
>>>>> timer
>>>>> interrupt increment on CPU 1. When using the DMA write to trigger
>>>>> execution,
>>>>> placing "sti"/"cli" around the polling routine improves the jitter
>>>>> substantially.
>>>>>
>>>>> Based on the above, is there some way to do one of the following:
>>>>>
>>>>> 1). Make a user space task higher priority than the timer interrupt
>>>>>
>>>>> or
>>>>>
>>>>> 2). A proper way to disable the local timer (vs. disabling all interrupts)
>>>>> on specific cores, as these cores would only need to run event based
>>>>> routines.
>>>> You can disable Xenomai timer interrupt by calling xnpod_stop_timer in
>>>> kernel-space. However, what you see in /proc/interrupt is not Xenomai
>>>> timer it is Linux', and it causes a bit of jitter (the time for the
>>>> I-pipe to mask, ack and return from interrupt). Disabling it would
>>>> require butchery in Linux code, but maybe simply masking the timer
>>>> interrupt could work.
>>>>
>>>> --
>>>> Gilles.
>>> I could not find any reference to the function xnpod_stop_timer in the
>>> xenomai code (searched through the cross-reference).
>>> I tried using xnarch_stop_timer(cpu), but this seems to disable the
>>> timers across all CPUs, rather than just the one passed.
>>> What I'd really like to do is simply mask the interrupt temporarily
>>> while my critical section is executing (the DMA polling routine)-- is
>>> there any way to do this? I can go into the local APIC and change the
>>> mask bits, but using some sort of API seems like it'd be cleaner.
>> xnpod_stop_timer no longer exists ! The function to disable irqs is
>> rt_intr_disable if you use the native skin.
>>
>> --
>> Gilles.
>>
>
> A couple of follow ups:
>
> 1). I have not been able to find the RT_INTR pointer associated with
> the local APIC timer interrupt-- is there some documentation on this?
> Basically, I would need something to pass to rt_intr_disable
Right, I was going to suggest to use xnintr_disable, but it will not
work either since there is no xnintr object associated with the local
clock. You have to use xnarch_disable_irq and pass the irq number of the
local APIC timer interrupt.
>
> 2). rt_intr_disable looks like it will disable the interrupt across
> all CPUs. Is there any way to disable the Xenomai local APIC timer
> handler on just a single CPU?
No, rt_intr_disable, xnintr_disable, xnarch_disable_irq only disable an
interrupt on the interrupt controller attached to the current cpu.
--
Gilles.
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