x86, apic: explain the purpose of max_physical_apicid
authorIngo Molnar <mingo@elte.hu>
Sat, 31 Jan 2009 02:57:12 +0000 (03:57 +0100)
committerIngo Molnar <mingo@elte.hu>
Thu, 5 Feb 2009 21:27:55 +0000 (22:27 +0100)
Signed-off-by: Ingo Molnar <mingo@elte.hu>
arch/x86/kernel/apic.c

index a04a73a51d20aefe92e797c603d773b60152b052..5475e1c31800f39260a20427c44b4fc5503343e2 100644 (file)
 #include <asm/smp.h>
 
 unsigned int num_processors;
+
 unsigned disabled_cpus __cpuinitdata;
+
 /* Processor that is doing the boot up */
 unsigned int boot_cpu_physical_apicid = -1U;
-EXPORT_SYMBOL(boot_cpu_physical_apicid);
+
+/*
+ * The highest APIC ID seen during enumeration.
+ *
+ * This determines the messaging protocol we can use: if all APIC IDs
+ * are in the 0 ... 7 range, then we can use logical addressing which
+ * has some performance advantages (better broadcasting).
+ *
+ * If there's an APIC ID above 8, we use physical addressing.
+ */
 unsigned int max_physical_apicid;
 
-/* Bitmask of physically existing CPUs */
+/*
+ * Bitmask of physically existing CPUs:
+ */
 physid_mask_t phys_cpu_present_map;
 
 /*