ROSSIER Daniel wrote:



2-       When a timer IRQ is received, we understood that the IRQ is ack'd and 
masked by handle_irq()
and sent to the domains through walk_pipeline() including Linux; but we have some doubts about that since the timer ISR of Linux first acknowledges the interrupt, and it seems that it acknowledges physically (hw ack); we expected that the acknowledgement would be a virtual ack in the Linux domain since the ack has been made previously by handle_irq(). In our case (ARM arch), the ack actually corresponds to a mask and therefore the timer IRQ is masked by Linux once it gets, and we then suspect some loss of timer interrupts.

have we understood correctly the mechanism? Any idea about this behaviour? Is 
it normal?

Still unclear to me; the ack would be done in the timer ISR; however in the 
(ARM) patch we have,
ipipe performs a hardware ack; I've seen in the x86 patch that adeos makes nothing within __ipipe_ack_system_irq().

Yes, it does actually, it's even its role as a fast acknowledge Adeos handler for incoming hw IRQs. It acks the APIC when the APIC support is built-in (I should have made the entire routine conditionally compiled on CONFIG_X86_LOCAL_APIC actually). Since __ipipe_ack_system_irq() is only called for APIC-controlled IRQs, this routine always touches the hw.

 I guess the last behaviour is correct, isn't it?


Looking at Stelian's code in arm/mach-integrator/core.c, I see that integrator_timer_interrupt does not acknowledge the timer IRQ, despite the misleading comment. It only makes some bookkeeping for TSC emulation when some higher domain in the pipeline has stolen the timer (e.g. Xenomai). Otherwise, when the Ipipe is compiled in, the regular timer tick handler does not touch the hw at all.

The logic is this one for all Adeos ports:

- some code intercepts the hw IRQs before they are passed to the regular Linux handlers, and feeds __ipipe_handle_irq() with those. - __ipipe_handle_irq() calls the fast acknowledge handler for the incoming hw IRQ, which ends up being, e.g. __ipipe_ack_system_irq() for APIC-controlled IRQs on x86 systems, or __ipipe_ack_timerirq() for the timer IRQ in the ARM Integrator/CP port. Some IRQs might need different fast ack handlers depending on their respective type. - IRQs are virtualized, which means that they are marked for delivery in the interrupt log, where they might linger for some time before the I-pipe is allowed to dispatch them to the proper handler eventually. - At some point in time, Linux ends up being notified of the IRQ, when higher priority domains are done with it (e.g. Xenomai). This means that the regular handler gets called, but Adeos ports always disable the vanilla acknowledge code from such handlers, so that we always have one and only one ack cycle for any given IRQ (i.e. the fast ack one from __ipipe_handle_irq).

--

Philippe.

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