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