Messages in this thread | | | Date | Wed, 4 Jun 2008 19:33:35 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 0/7] Boot IRQ quirks and rerouting |
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On Wed, 4 Jun 2008, Maciej W. Rozycki wrote: > On Wed, 4 Jun 2008, Thomas Gleixner wrote: > > > It does matter. When the interrupt is _not_ handled then it comes back > > immediately for ever and after a while the kernel decides to disable > > the legacy int, because nobody cares about the interrupt. > > Mental shortcut, sorry -- making the interrupt be discarded through the > primary rather than the secondary, etc. I/O APIC does not change anything. > Based on the description of the problem, the interupt will just have to be > delivered somewhere, so I see little purpose in complicating the routing > and causing additional sharing just to discard the interrupt elsewhere > anyway. If INTx messages cannot be blocked on the way anywhere, then the > originating I/O APIC should never get its inputs masked and the handler > should take care of the unwanted interrupts there. This is at least my > opinion.
There is no way to take care of an unwanted interrupt when there is no handler which knows to deal with the device.
The problem case is mostly preempt-rt, where we receive the interrupt, mask it and wake up the handler thread. We can not leave it unmasked for obvious reasons.
> BTW, it could be possible to mask the interrupt by fiddling with the > vector used and the TPR instead -- we have a range of low-priority vectors > which are never used for APIC interrupts, so the TPR may be hardcoded to > some non-zero value for all systems and then for the problematic chipsets > handlers may change vectors to mask or unmask APIC interrupts. This would > have to be verified on actual hardware and be conditional as it is likely > to cause troubles for systems using serial interrupt delivery over the > inter-APIC bus (the vector, delivery mode, etc. are generally not meant to > be changed with the input unmasked for these chips -- which just shows how > braindead the idea of the mask having side effects is). Just a thought.
I tried this already and it results in extremly strange and randomly changing behaviour up to a full system lockup :(
Thanks,
tglx
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