[PATCH] cpu_relax(): smpboot.c

Add cpu_relax() to various smpboot.c init loops.  cpu_relax() always implies a
barrier (according to Arjan), so remove those as well.

Signed-off-by: Andreas Mohr <andi@lisas.de>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 6 deletions

diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index 825b2b4ca721..bd0ca5c9f053 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -257,7 +257,7 @@ static void __init synchronize_tsc_bp (void)
                  * all APs synchronize but they loop on '== num_cpus'
                  */
                 while (atomic_read(&tsc_count_start) != num_booting_cpus()-1)
-                        mb();
+                        cpu_relax();
                 atomic_set(&tsc_count_stop, 0);
                 wmb();
                 /*
@@ -276,7 +276,7 @@ static void __init synchronize_tsc_bp (void)
                  * Wait for all APs to leave the synchronization point:
                  */
                 while (atomic_read(&tsc_count_stop) != num_booting_cpus()-1)
-                        mb();
+                        cpu_relax();
                 atomic_set(&tsc_count_start, 0);
                 wmb();
                 atomic_inc(&tsc_count_stop);
@@ -333,19 +333,21 @@ static void __init synchronize_tsc_ap (void)
          * this gets called, so we first wait for the BP to
          * finish SMP initialization:
          */
-        while (!atomic_read(&tsc_start_flag)) mb();
+        while (!atomic_read(&tsc_start_flag))
+                cpu_relax();
 
         for (i = 0; i < NR_LOOPS; i++) {
                 atomic_inc(&tsc_count_start);
                 while (atomic_read(&tsc_count_start) != num_booting_cpus())
-                        mb();
+                        cpu_relax();
 
                 rdtscll(tsc_values[smp_processor_id()]);
                 if (i == NR_LOOPS-1)
                         write_tsc(0, 0);
 
                 atomic_inc(&tsc_count_stop);
-                while (atomic_read(&tsc_count_stop) != num_booting_cpus()) mb();
+                while (atomic_read(&tsc_count_stop) != num_booting_cpus())
+                        cpu_relax();
         }
 }
 #undef NR_LOOPS
@@ -1433,7 +1435,7 @@ int __devinit __cpu_up(unsigned int cpu)
         /* Unleash the CPU! */
         cpu_set(cpu, smp_commenced_mask);
         while (!cpu_isset(cpu, cpu_online_map))
-                mb();
+                cpu_relax();
         return 0;
 }