[PATCH] ia64: update Kconfig comment for NR_CPUS

arch/ia64/Kconfig

@@ -424,9 +424,15 @@ config EFI_VARS
 	  support" (CONFIG_PROC_FS) is enabled, too.
 
 config NR_CPUS
-	int "Maximum number of CPUs (2-64)"
+	int "Maximum number of CPUs"
 	depends on SMP
 	default "64"
+	help
+	  You should set this to the number of CPUs in your system, but
+	  keep in mind that a kernel compiled for, e.g., 2 CPUs will boot but
+	  only use 2 CPUs on a >2 CPU system.  Setting this to a value larger
+	  than 64 will cause the use of a CPU mask array, causing a small
+	  performance hit.
 
 source "fs/Kconfig.binfmt"