[PATCH -v2 5/5] x86: use dmi check to treat disabled cpus as hotplug cpus.

[Yinghai Lu <yinghai@kernel.org>]

some systems that have disable cpus entries because same
  BIOS will support 2 sockets and 4 sockets and more at
  same time, BIOS just leave some disable entries, but
  those system do not support cpu hotplug. we don't need
  treat disabled_cpus as hotplug cpus.
so we can make nr_cpu_ids smaller and save more space
  (pcpu data allocations), and could make some systems run
  with logical flat instead of physical flat apic mode

-v2: change to black list instead

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
 arch/x86/kernel/smpboot.c |   76 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 74 insertions(+), 2 deletions(-)

Index: linux-2.6/arch/x86/kernel/smpboot.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/smpboot.c
+++ linux-2.6/arch/x86/kernel/smpboot.c
@@ -47,6 +47,7 @@
 #include <linux/bootmem.h>
 #include <linux/err.h>
 #include <linux/nmi.h>
+#include <linux/dmi.h>
 #include <linux/tboot.h>
 
 #include <asm/acpi.h>
@@ -1178,6 +1179,59 @@ static int __init _setup_possible_cpus(c
 }
 early_param("possible_cpus", _setup_possible_cpus);
 
+static __initdata int treat_disabled_cpus_as_hotplug = 1;
+static __init int hotplug_cpus_check(const struct dmi_system_id *d)
+{
+        printk(KERN_NOTICE "%s detected: treat disabled cpus as hotplug ones\n", d->ident);
+        treat_disabled_cpus_as_hotplug = 0;
+
+        return 0;
+}
+
+static struct dmi_system_id hotplug_cpus_dmi_table[] __initdata = {
+        {
+                .callback = hotplug_cpus_check,
+                .ident = "Sun Microsystems Sun Fire X4440",
+                .matches = {
+                        DMI_MATCH(DMI_SYS_VENDOR, "Sun Microsystems"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Sun Fire X4440"),
+                },
+        },
+        {
+                .callback = hotplug_cpus_check,
+                .ident = "Sun Microsystems Sun Fire X4240",
+                .matches = {
+                        DMI_MATCH(DMI_SYS_VENDOR, "Sun Microsystems"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Sun Fire X4240"),
+                },
+        },
+        {
+                .callback = hotplug_cpus_check,
+                .ident = "Sun Microsystems Sun Fire X4140",
+                .matches = {
+                        DMI_MATCH(DMI_SYS_VENDOR, "Sun Microsystems"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Sun Fire X4140"),
+                },
+        },
+        {
+                .callback = hotplug_cpus_check,
+                .ident = "Sun Microsystems Sun Fire X4600",
+                .matches = {
+                        DMI_MATCH(DMI_SYS_VENDOR, "Sun Microsystems"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Sun Fire X4600"),
+                },
+        },
+        {
+                .callback = hotplug_cpus_check,
+                .ident = "Sun Microsystems Sun Fire X4640",
+                .matches = {
+                        DMI_MATCH(DMI_SYS_VENDOR, "Sun Microsystems"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Sun Fire X4640"),
+                },
+        },
+        { } /* NULL entry stops DMI scanning */
+};
+
 
 /*
  * cpu_possible_mask should be static, it cannot change as cpu's
@@ -1204,8 +1258,26 @@ __init void prefill_possible_map(void)
 	if (!num_processors)
 		num_processors = 1;
 
-	if (setup_possible_cpus == -1)
-		possible = num_processors + disabled_cpus;
+	if (setup_possible_cpus == -1) {
+		possible = num_processors;
+		/*
+		 * do we have better way to detect hotplug cpus?
+		 *
+		 * some systems that have disable cpus entries because same
+		 *  BIOS will support 2 sockets and 4 sockets and more at
+		 *  same time, BIOS just leave some disabled entries with wild
+		 *  apicid, but those system do not support cpu hotplug.
+		 *  we don't need treat disabled_cpus as hotplug cpus.
+		 * so we can make nr_cpu_ids smaller and save more space
+		 *  (pcpu data allocations), and could make some systems run
+		 *  with logical flat instead of physical flat apic mode
+		 */
+		if (disabled_cpus) {
+			dmi_check_system(hotplug_cpus_dmi_table);
+			if (treat_disabled_cpus_as_hotplug)
+				possible += disabled_cpus;
+		}
+	}
 	else
 		possible = setup_possible_cpus;