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Diffstat (limited to 'Documentation/i386/IO-APIC.txt')
| -rw-r--r-- | Documentation/i386/IO-APIC.txt | 32 |
1 files changed, 17 insertions, 15 deletions
diff --git a/Documentation/i386/IO-APIC.txt b/Documentation/i386/IO-APIC.txt index 435e69e6e9a..f95166645d2 100644 --- a/Documentation/i386/IO-APIC.txt +++ b/Documentation/i386/IO-APIC.txt @@ -1,12 +1,14 @@ Most (all) Intel-MP compliant SMP boards have the so-called 'IO-APIC', -which is an enhanced interrupt controller, it enables us to route -hardware interrupts to multiple CPUs, or to CPU groups. +which is an enhanced interrupt controller. It enables us to route +hardware interrupts to multiple CPUs, or to CPU groups. Without an +IO-APIC, interrupts from hardware will be delivered only to the +CPU which boots the operating system (usually CPU#0). Linux supports all variants of compliant SMP boards, including ones with -multiple IO-APICs. (multiple IO-APICs are used in high-end servers to -distribute IRQ load further). +multiple IO-APICs. Multiple IO-APICs are used in high-end servers to +distribute IRQ load further. -There are (a few) known breakages in certain older boards, which bugs are +There are (a few) known breakages in certain older boards, such bugs are usually worked around by the kernel. If your MP-compliant SMP board does not boot Linux, then consult the linux-smp mailing list archives first. @@ -28,18 +30,18 @@ If your box boots fine with enabled IO-APIC IRQs, then your hell:~> <---------------------------- -some interrupts are still listed as 'XT PIC', but this is not a problem, +Some interrupts are still listed as 'XT PIC', but this is not a problem; none of those IRQ sources is performance-critical. -in the unlikely case that your board does not create a working mp-table, +In the unlikely case that your board does not create a working mp-table, you can use the pirq= boot parameter to 'hand-construct' IRQ entries. This -is nontrivial though and cannot be automated. One sample /etc/lilo.conf +is non-trivial though and cannot be automated. One sample /etc/lilo.conf entry: append="pirq=15,11,10" -the actual numbers depend on your system, on your PCI cards and on their +The actual numbers depend on your system, on your PCI cards and on their PCI slot position. Usually PCI slots are 'daisy chained' before they are connected to the PCI chipset IRQ routing facility (the incoming PIRQ1-4 lines): @@ -54,7 +56,7 @@ lines): PIRQ1 ----| |- `----| |- `----| |- `----| |--------| | `-' `-' `-' `-' `-' -every PCI card emits a PCI IRQ, which can be INTA,INTB,INTC,INTD: +Every PCI card emits a PCI IRQ, which can be INTA, INTB, INTC or INTD: ,-. INTD--| | @@ -95,21 +97,21 @@ card (IRQ11) in Slot3, and have Slot1 empty: [value '0' is a generic 'placeholder', reserved for empty (or non-IRQ emitting) slots.] -generally, it's always possible to find out the correct pirq= settings, just +Generally, it's always possible to find out the correct pirq= settings, just permute all IRQ numbers properly ... it will take some time though. An 'incorrect' pirq line will cause the booting process to hang, or a device -won't function properly (if it's inserted as eg. a module). +won't function properly (e.g. if it's inserted as a module). -If you have 2 PCI buses, then you can use up to 8 pirq values. Although such +If you have 2 PCI buses, then you can use up to 8 pirq values, although such boards tend to have a good configuration. Be prepared that it might happen that you need some strange pirq line: append="pirq=0,0,0,0,0,0,9,11" -use smart try-and-err techniques to find out the correct pirq line ... +Use smart trial-and-error techniques to find out the correct pirq line ... -good luck and mail to linux-smp@vger.kernel.org or +Good luck and mail to linux-smp@vger.kernel.org or linux-kernel@vger.kernel.org if you have any problems that are not covered by this document. |