[PATCH] i386/x86-64: Share interrupt vectors when there is a large number of interrupt sources

Here's a patch that builds on Natalie Protasevich's IRQ compression
patch and tries to work for MPS boots as well as ACPI.  It is meant for
a 4-node IBM x460 NUMA box, which was dying because it had interrupt
pins with GSI numbers > NR_IRQS and thus overflowed irq_desc.

The problem is that this system has 270 GSIs (which are 1:1 mapped with
I/O APIC RTEs) and an 8-node box would have 540.  This is much bigger
than NR_IRQS (224 for both i386 and x86_64).  Also, there aren't enough
vectors to go around.  There are about 190 usable vectors, not counting
the reserved ones and the unused vectors at 0x20 to 0x2F.  So, my patch
attempts to compress the GSI range and share vectors by sharing IRQs.

Cc: "Protasevich, Natalie" <Natalie.Protasevich@unisys.com>

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 5 insertions, 1 deletions

diff --git a/include/asm-x86_64/desc.h b/include/asm-x86_64/desc.h
index 68ac3c62fe3d..1a3d380f9d5d 100644
--- a/include/asm-x86_64/desc.h
+++ b/include/asm-x86_64/desc.h
@@ -98,16 +98,19 @@ static inline void _set_gate(void *adr, unsigned type, unsigned long func, unsig
 
 static inline void set_intr_gate(int nr, void *func) 
 { 
+        BUG_ON((unsigned)nr > 0xFF);
         _set_gate(&idt_table[nr], GATE_INTERRUPT, (unsigned long) func, 0, 0); 
 } 
 
 static inline void set_intr_gate_ist(int nr, void *func, unsigned ist) 
 { 
+        BUG_ON((unsigned)nr > 0xFF);
         _set_gate(&idt_table[nr], GATE_INTERRUPT, (unsigned long) func, 0, ist); 
 } 
 
 static inline void set_system_gate(int nr, void *func) 
 { 
+        BUG_ON((unsigned)nr > 0xFF);
         _set_gate(&idt_table[nr], GATE_INTERRUPT, (unsigned long) func, 3, 0); 
 } 
 
diff --git a/include/asm-x86_64/mpspec.h b/include/asm-x86_64/mpspec.h
index f267e10c023d..6b375384f5c2 100644
--- a/include/asm-x86_64/mpspec.h
+++ b/include/asm-x86_64/mpspec.h
@@ -157,7 +157,8 @@ struct mpc_config_lintsrc
  */
 
 #define MAX_MP_BUSSES 256
-#define MAX_IRQ_SOURCES 256
+/* Each PCI slot may be a combo card with its own bus.  4 IRQ pins per slot. */
+#define MAX_IRQ_SOURCES (MAX_MP_BUSSES * 4)
 enum mp_bustype {
         MP_BUS_ISA = 1,
         MP_BUS_EISA,