[PATCH] x86_64: Dont use broadcast shortcut to make it cpu hotplug safe.

Broadcast IPI's provide un-expected behaviour for cpu hotplug.  CPU's in
offline state also end up receiving the IPI.  Once the cpus become online they
receive these stale IPI's which are bad and introduce unexpected behaviour.

This is easily avoided by not sending a broadcast and addressing just the
CPU's in online map.  Doing prelim cycle counts it appears there is no big
overhead and numbers seem around 0x3000-0x3900 on an average on x86 and x86_64
systems with CPUS running 3G, both for broadcast and mask version of the
API's.

The shortcuts are useful only for flat mode (where the perf shows no
degradation), and in cluster mode, its unicast anyway.  Its simpler to just
not use broadcast anymore.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Acked-by: Andi Kleen <ak@muc.de>
Acked-by: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 18 insertions, 1 deletions

diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
index 571a55462fa0..b969ee128728 100644
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -508,9 +508,22 @@ void __cpuinit start_secondary(void)
         set_cpu_sibling_map(smp_processor_id());
 
         /*
+         * We need to hold call_lock, so there is no inconsistency
+         * between the time smp_call_function() determines number of
+         * IPI receipients, and the time when the determination is made
+         * for which cpus receive the IPI in genapic_flat.c. Holding this
+         * lock helps us to not include this cpu in a currently in progress
+         * smp_call_function().
+         */
+        lock_ipi_call_lock();
+
+        /*
          * Allow the master to continue.
          */
         cpu_set(smp_processor_id(), cpu_online_map);
+        per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
+        unlock_ipi_call_lock();
+
         mb();
 
         /* Wait for TSC sync to not schedule things before.
@@ -1038,6 +1051,7 @@ void __init smp_prepare_boot_cpu(void)
         cpu_set(me, cpu_callout_map);
         cpu_set(0, cpu_sibling_map[0]);
         cpu_set(0, cpu_core_map[0]);
+        per_cpu(cpu_state, me) = CPU_ONLINE;
 }
 
 /*
@@ -1066,6 +1080,7 @@ int __cpuinit __cpu_up(unsigned int cpu)
                 return -ENOSYS;
         }
 
+        per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
         /* Boot it! */
         err = do_boot_cpu(cpu, apicid);
         if (err < 0) {
@@ -1170,8 +1185,10 @@ void __cpu_die(unsigned int cpu)
 
         for (i = 0; i < 10; i++) {
                 /* They ack this in play_dead by setting CPU_DEAD */
-                if (per_cpu(cpu_state, cpu) == CPU_DEAD)
+                if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
+                        printk ("CPU %d is now offline\n", cpu);
                         return;
+                }
                 current->state = TASK_UNINTERRUPTIBLE;
                 schedule_timeout(HZ/10);
         }