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1da177e4 LT |
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. | |
4 | ||
5 | Linux supports all variants of compliant SMP boards, including ones with | |
6 | multiple IO-APICs. (multiple IO-APICs are used in high-end servers to | |
7 | distribute IRQ load further). | |
8 | ||
9 | There are (a few) known breakages in certain older boards, which bugs are | |
10 | usually worked around by the kernel. If your MP-compliant SMP board does | |
11 | not boot Linux, then consult the linux-smp mailing list archives first. | |
12 | ||
13 | If your box boots fine with enabled IO-APIC IRQs, then your | |
14 | /proc/interrupts will look like this one: | |
15 | ||
16 | ----------------------------> | |
17 | hell:~> cat /proc/interrupts | |
18 | CPU0 | |
19 | 0: 1360293 IO-APIC-edge timer | |
20 | 1: 4 IO-APIC-edge keyboard | |
21 | 2: 0 XT-PIC cascade | |
22 | 13: 1 XT-PIC fpu | |
23 | 14: 1448 IO-APIC-edge ide0 | |
24 | 16: 28232 IO-APIC-level Intel EtherExpress Pro 10/100 Ethernet | |
25 | 17: 51304 IO-APIC-level eth0 | |
26 | NMI: 0 | |
27 | ERR: 0 | |
28 | hell:~> | |
29 | <---------------------------- | |
30 | ||
31 | some interrupts are still listed as 'XT PIC', but this is not a problem, | |
32 | none of those IRQ sources is performance-critical. | |
33 | ||
34 | ||
35 | in the unlikely case that your board does not create a working mp-table, | |
36 | you can use the pirq= boot parameter to 'hand-construct' IRQ entries. This | |
37 | is nontrivial though and cannot be automated. One sample /etc/lilo.conf | |
38 | entry: | |
39 | ||
40 | append="pirq=15,11,10" | |
41 | ||
42 | the actual numbers depend on your system, on your PCI cards and on their | |
43 | PCI slot position. Usually PCI slots are 'daisy chained' before they are | |
44 | connected to the PCI chipset IRQ routing facility (the incoming PIRQ1-4 | |
45 | lines): | |
46 | ||
47 | ,-. ,-. ,-. ,-. ,-. | |
48 | PIRQ4 ----| |-. ,-| |-. ,-| |-. ,-| |--------| | | |
49 | |S| \ / |S| \ / |S| \ / |S| |S| | |
50 | PIRQ3 ----|l|-. `/---|l|-. `/---|l|-. `/---|l|--------|l| | |
51 | |o| \/ |o| \/ |o| \/ |o| |o| | |
52 | PIRQ2 ----|t|-./`----|t|-./`----|t|-./`----|t|--------|t| | |
53 | |1| /\ |2| /\ |3| /\ |4| |5| | |
54 | PIRQ1 ----| |- `----| |- `----| |- `----| |--------| | | |
55 | `-' `-' `-' `-' `-' | |
56 | ||
57 | every PCI card emits a PCI IRQ, which can be INTA,INTB,INTC,INTD: | |
58 | ||
59 | ,-. | |
60 | INTD--| | | |
61 | |S| | |
62 | INTC--|l| | |
63 | |o| | |
64 | INTB--|t| | |
65 | |x| | |
66 | INTA--| | | |
67 | `-' | |
68 | ||
69 | These INTA-D PCI IRQs are always 'local to the card', their real meaning | |
70 | depends on which slot they are in. If you look at the daisy chaining diagram, | |
71 | a card in slot4, issuing INTA IRQ, it will end up as a signal on PIRQ2 of | |
72 | the PCI chipset. Most cards issue INTA, this creates optimal distribution | |
73 | between the PIRQ lines. (distributing IRQ sources properly is not a | |
74 | necessity, PCI IRQs can be shared at will, but it's a good for performance | |
75 | to have non shared interrupts). Slot5 should be used for videocards, they | |
76 | do not use interrupts normally, thus they are not daisy chained either. | |
77 | ||
78 | so if you have your SCSI card (IRQ11) in Slot1, Tulip card (IRQ9) in | |
79 | Slot2, then you'll have to specify this pirq= line: | |
80 | ||
81 | append="pirq=11,9" | |
82 | ||
83 | the following script tries to figure out such a default pirq= line from | |
84 | your PCI configuration: | |
85 | ||
86 | echo -n pirq=; echo `scanpci | grep T_L | cut -c56-` | sed 's/ /,/g' | |
87 | ||
88 | note that this script wont work if you have skipped a few slots or if your | |
89 | board does not do default daisy-chaining. (or the IO-APIC has the PIRQ pins | |
90 | connected in some strange way). E.g. if in the above case you have your SCSI | |
91 | card (IRQ11) in Slot3, and have Slot1 empty: | |
92 | ||
93 | append="pirq=0,9,11" | |
94 | ||
95 | [value '0' is a generic 'placeholder', reserved for empty (or non-IRQ emitting) | |
96 | slots.] | |
97 | ||
98 | generally, it's always possible to find out the correct pirq= settings, just | |
99 | permute all IRQ numbers properly ... it will take some time though. An | |
100 | 'incorrect' pirq line will cause the booting process to hang, or a device | |
101 | won't function properly (if it's inserted as eg. a module). | |
102 | ||
103 | If you have 2 PCI buses, then you can use up to 8 pirq values. Although such | |
104 | boards tend to have a good configuration. | |
105 | ||
106 | Be prepared that it might happen that you need some strange pirq line: | |
107 | ||
108 | append="pirq=0,0,0,0,0,0,9,11" | |
109 | ||
110 | use smart try-and-err techniques to find out the correct pirq line ... | |
111 | ||
112 | good luck and mail to linux-smp@vger.kernel.org or | |
113 | linux-kernel@vger.kernel.org if you have any problems that are not covered | |
114 | by this document. | |
115 | ||
116 | -- mingo | |
117 |