On Thu, 31 Oct 2019, Bjorn Helgaas wrote: > On Thu, Oct 31, 2019 at 03:53:50AM +0000, Kar Hin Ong wrote: > > I've an Intel Haswell system running Linux kernel v4.14 with > > preempt_rt patch. The system contain 2 IOAPICs: IOAPIC 1 is on the > > PCH where IOAPIC 2 is on the CPU. > > > > I observed that whenever a PCI device is firing interrupt (INTx) to > > Pin 20 of IOAPIC 2 (GSI 44); the kernel will receives 2 interrupts: > > 1. Interrupt from Pin 20 of IOAPIC 2 -> Expected > > 2. Interrupt from Pin 19 of IOAPIC 1 -> UNEXPECTED, erroneously > > triggered > > > > The unexpected interrupt is unhandled eventually. When this scenario > > happen more than 99,000 times, kernel disables the interrupt line > > (Pin 19 of IOAPIC 1) and causing device that has requested it become > > malfunction. > > > > I managed to also reproduced this issue on RHEL 8 and Ubuntu 19-04 > > (without preempt_rt patch) after added "threadirqs" to the kernel > > command line. > > > > After digging further, I noticed that the said issue is happened > > whenever an interrupt pin on IOAPIC 2 is masked: > > - Masking Pin 20 of IOAPIC 2 triggers Pin 19 of IOAPIC 1 > > - Masking Pin 22 of IOAPIC 2 triggers Pin 18 of IOAPIC 1 This is pretty much the same problem which we had analyzed and worked around years ago. > > From Intel Xeon Processor E5/E7 v3 Product Family External Design > > Specification (EDS), Volume One: Architecture, section 13.1 (Legacy > > PCI Interrupt Handling), it mention: "If the I/OxAPIC entry is > > masked (via the 'mask' bit in the corresponding Redirection Table > > Entry), then the corresponding PCI Express interrupt(s) is forwarded > > to the legacy PCH" Oh well. Really useful behaviour - NOT! > > I would like to understand if my interpretation is make sense. If > > yes, should the "oneshot" algorithm need to be updated to support > > Haswell system? No. You cannot change the oneshot algorithm. The workarounds for this are enabled by PCI quirls and either CONFIG_X86_REROUTE_FOR_BROKEN_BOOT_IRQS=y or 'ioapicreroute' on the command line. It might be wortha try to add the PCI ID of that box to the quirk list, i.e. the PCI ID matches in drivers/pci/quirks.c which belong to the function: quirk_reroute_to_boot_interrupts_intel(). Thanks, tglx
