[PATCH] i386: Dont use IPI broadcast when using cpu hotplug.

This patch introduces a startup parameter no_broadcast.  When we enable
CONFIG_HOTPLUG_CPU, we dont want to use broadcast shortcut as it has ill
effects on a offline cpu.  If we issue broadcast, the IPI is also delivered
to offline cpus, or partially up cpu causing stale IPI's to be handled,
which is a problem and can cause undesirable effects.

Introduces a new startup cmdline option no_ipi_broadcast, that can be
switched at cmdline if necessary.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Acked-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 52 insertions, 2 deletions

diff --git a/arch/i386/mach-default/setup.c b/arch/i386/mach-default/setup.c
index 0aa08eaa8932..e5a1a83d09ef 100644
--- a/arch/i386/mach-default/setup.c
+++ b/arch/i386/mach-default/setup.c
@@ -10,6 +10,14 @@
 #include <asm/acpi.h>
 #include <asm/arch_hooks.h>
 
+#ifdef CONFIG_HOTPLUG_CPU
+#define DEFAULT_SEND_IPI        (1)
+#else
+#define DEFAULT_SEND_IPI        (0)
+#endif
+
+int no_broadcast=DEFAULT_SEND_IPI;
+
 /**
  * pre_intr_init_hook - initialisation prior to setting up interrupt vectors
  *
@@ -104,3 +112,22 @@ void __init mca_nmi_hook(void)
         printk("NMI generated from unknown source!\n");
 }
 #endif
+
+static __init int no_ipi_broadcast(char *str)
+{
+        get_option(&str, &no_broadcast);
+        printk ("Using %s mode\n", no_broadcast ? "No IPI Broadcast" :
+                                                                                        "IPI Broadcast");
+        return 1;
+}
+
+__setup("no_ipi_broadcast", no_ipi_broadcast);
+
+static int __init print_ipi_mode(void)
+{
+        printk ("Using IPI %s mode\n", no_broadcast ? "No-Shortcut" :
+                                                                                        "Shortcut");
+        return 0;
+}
+
+late_initcall(print_ipi_mode);
diff --git a/include/asm-i386/mach-default/mach_ipi.h b/include/asm-i386/mach-default/mach_ipi.h
index 6f2b17a20089..cc756a67cd63 100644
--- a/include/asm-i386/mach-default/mach_ipi.h
+++ b/include/asm-i386/mach-default/mach_ipi.h
@@ -4,11 +4,34 @@
 void send_IPI_mask_bitmask(cpumask_t mask, int vector);
 void __send_IPI_shortcut(unsigned int shortcut, int vector);
 
+extern int no_broadcast;
+
 static inline void send_IPI_mask(cpumask_t mask, int vector)
 {
         send_IPI_mask_bitmask(mask, vector);
 }
 
+static inline void __local_send_IPI_allbutself(int vector)
+{
+        if (no_broadcast) {
+                cpumask_t mask = cpu_online_map;
+                int this_cpu = get_cpu();
+
+                cpu_clear(this_cpu, mask);
+                send_IPI_mask(mask, vector);
+                put_cpu();
+        } else
+                __send_IPI_shortcut(APIC_DEST_ALLBUT, vector);
+}
+
+static inline void __local_send_IPI_all(int vector)
+{
+        if (no_broadcast)
+                send_IPI_mask(cpu_online_map, vector);
+        else
+                __send_IPI_shortcut(APIC_DEST_ALLINC, vector);
+}
+
 static inline void send_IPI_allbutself(int vector)
 {
         /*
@@ -18,13 +41,13 @@ static inline void send_IPI_allbutself(int vector)
         if (!(num_online_cpus() > 1))
                 return;
 
-        __send_IPI_shortcut(APIC_DEST_ALLBUT, vector);
+        __local_send_IPI_allbutself(vector);
         return;
 }
 
 static inline void send_IPI_all(int vector)
 {
-        __send_IPI_shortcut(APIC_DEST_ALLINC, vector);
+        __local_send_IPI_all(vector);
 }
 
 #endif /* __ASM_MACH_IPI_H */