Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 Most (all) Intel-MP compliant SMP boards have the so-called 'IO-APIC', 2 which is an enhanced interrupt controller. It enables us to route 3 hardware interrupts to multiple CPUs, or to CPU groups. Without an 4 IO-APIC, interrupts from hardware will be delivered only to the 5 CPU which boots the operating system (usually CPU#0). 6 7 Linux supports all variants of compliant SMP boards, including ones with 8 multiple IO-APICs. Multiple IO-APICs are used in high-end servers to 9 distribute IRQ load further. 10 11 There are (a few) known breakages in certain older boards, such bugs are 12 usually worked around by the kernel. If your MP-compliant SMP board does 13 not boot Linux, then consult the linux-smp mailing list archives first. 14 15 If your box boots fine with enabled IO-APIC IRQs, then your 16 /proc/interrupts will look like this one: 17 18 ----------------------------> 19 hell:~> cat /proc/interrupts 20 CPU0 21 0: 1360293 IO-APIC-edge timer 22 1: 4 IO-APIC-edge keyboard 23 2: 0 XT-PIC cascade 24 13: 1 XT-PIC fpu 25 14: 1448 IO-APIC-edge ide0 26 16: 28232 IO-APIC-level Intel EtherExpress Pro 10/100 Ethernet 27 17: 51304 IO-APIC-level eth0 28 NMI: 0 29 ERR: 0 30 hell:~> 31 <---------------------------- 32 33 Some interrupts are still listed as 'XT PIC', but this is not a problem; 34 none of those IRQ sources is performance-critical. 35 36 37 In the unlikely case that your board does not create a working mp-table, 38 you can use the pirq= boot parameter to 'hand-construct' IRQ entries. This 39 is non-trivial though and cannot be automated. One sample /etc/lilo.conf 40 entry: 41 42 append="pirq=15,11,10" 43 44 The actual numbers depend on your system, on your PCI cards and on their 45 PCI slot position. Usually PCI slots are 'daisy chained' before they are 46 connected to the PCI chipset IRQ routing facility (the incoming PIRQ1-4 47 lines): 48 49 ,-. ,-. ,-. ,-. ,-. 50 PIRQ4 ----| |-. ,-| |-. ,-| |-. ,-| |--------| | 51 |S| \ / |S| \ / |S| \ / |S| |S| 52 PIRQ3 ----|l|-. `/---|l|-. `/---|l|-. `/---|l|--------|l| 53 |o| \/ |o| \/ |o| \/ |o| |o| 54 PIRQ2 ----|t|-./`----|t|-./`----|t|-./`----|t|--------|t| 55 |1| /\ |2| /\ |3| /\ |4| |5| 56 PIRQ1 ----| |- `----| |- `----| |- `----| |--------| | 57 `-' `-' `-' `-' `-' 58 59 Every PCI card emits a PCI IRQ, which can be INTA, INTB, INTC or INTD: 60 61 ,-. 62 INTD--| | 63 |S| 64 INTC--|l| 65 |o| 66 INTB--|t| 67 |x| 68 INTA--| | 69 `-' 70 71 These INTA-D PCI IRQs are always 'local to the card', their real meaning 72 depends on which slot they are in. If you look at the daisy chaining diagram, 73 a card in slot4, issuing INTA IRQ, it will end up as a signal on PIRQ4 of 74 the PCI chipset. Most cards issue INTA, this creates optimal distribution 75 between the PIRQ lines. (distributing IRQ sources properly is not a 76 necessity, PCI IRQs can be shared at will, but it's a good for performance 77 to have non shared interrupts). Slot5 should be used for videocards, they 78 do not use interrupts normally, thus they are not daisy chained either. 79 80 so if you have your SCSI card (IRQ11) in Slot1, Tulip card (IRQ9) in 81 Slot2, then you'll have to specify this pirq= line: 82 83 append="pirq=11,9" 84 85 the following script tries to figure out such a default pirq= line from 86 your PCI configuration: 87 88 echo -n pirq=; echo `scanpci | grep T_L | cut -c56-` | sed 's/ /,/g' 89 90 note that this script won't work if you have skipped a few slots or if your 91 board does not do default daisy-chaining. (or the IO-APIC has the PIRQ pins 92 connected in some strange way). E.g. if in the above case you have your SCSI 93 card (IRQ11) in Slot3, and have Slot1 empty: 94 95 append="pirq=0,9,11" 96 97 [value '0' is a generic 'placeholder', reserved for empty (or non-IRQ emitting) 98 slots.] 99 100 Generally, it's always possible to find out the correct pirq= settings, just 101 permute all IRQ numbers properly ... it will take some time though. An 102 'incorrect' pirq line will cause the booting process to hang, or a device 103 won't function properly (e.g. if it's inserted as a module). 104 105 If you have 2 PCI buses, then you can use up to 8 pirq values, although such 106 boards tend to have a good configuration. 107 108 Be prepared that it might happen that you need some strange pirq line: 109 110 append="pirq=0,0,0,0,0,0,9,11" 111 112 Use smart trial-and-error techniques to find out the correct pirq line ... 113 114 Good luck and mail to linux-smp@vger.kernel.org or 115 linux-kernel@vger.kernel.org if you have any problems that are not covered 116 by this document. 117 118 -- mingo