[PATCH] genirq: irq: generalize the check for HARDIRQ_BITS This patch adds support for systems that cannot receive every interrupt on a single cpu simultaneously, in the check to see if we have enough HARDIRQ_BITS. MAX_HARDIRQS_PER_CPU becomes the count of the maximum number of hardare generated interrupts per cpu. On architectures that support per cpu interrupt delivery this can be a significant space savings and scalability bonus. This patch adds support for systems that cannot receive every interrupt on Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Rajesh Shah <rajesh.shah@intel.com> Cc: Andi Kleen <ak@muc.de> Cc: "Protasevich, Natalie" <Natalie.Protasevich@UNISYS.com> Cc: "Luck, Tony" <tony.luck@intel.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/asm-x86_64/hardirq.h b/include/asm-x86_64/hardirq.h
index 64a65ce..95d5e09 100644
--- a/include/asm-x86_64/hardirq.h
+++ b/include/asm-x86_64/hardirq.h

@@ -6,6 +6,9 @@
 #include <asm/pda.h>
 #include <asm/apic.h>
 
+/* We can have at most NR_VECTORS irqs routed to a cpu at a time */
+#define MAX_HARDIRQS_PER_CPU NR_VECTORS
+
 #define __ARCH_IRQ_STAT 1
 
 #define local_softirq_pending() read_pda(__softirq_pending)

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 50d8b57..612472a 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h

@@ -28,11 +28,16 @@
 
 #ifndef HARDIRQ_BITS
 #define HARDIRQ_BITS	12
+
+#ifndef MAX_HARDIRQS_PER_CPU
+#define MAX_HARDIRQS_PER_CPU NR_IRQS
+#endif
+
 /*
  * The hardirq mask has to be large enough to have space for potentially
  * all IRQ sources in the system nesting on a single CPU.
  */
-#if (1 << HARDIRQ_BITS) < NR_IRQS
+#if (1 << HARDIRQ_BITS) < MAX_HARDIRQS_PER_CPU
 # error HARDIRQ_BITS is too low!
 #endif
 #endif