metag: smp: don't spin waiting for CPU to start

Use a completion to block until a secondary CPU has started up, like ARM
do, instead of a loop of udelays.

On Meta, SMP is really SMT, with each "CPU" being a different hardware
thread on the same Meta processor core, so as well as being more
efficient and latency friendly, using a completion prevents the bogomips
of the secondary CPU from being drastically skewed every time by the
execution of the tight in-cache udelay loop on the other CPU.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>

1 files changed, 6 insertions, 10 deletions

diff --git a/arch/metag/kernel/smp.c b/arch/metag/kernel/smp.c
index 09979f203a4d..e413875cf6d2 100644
--- a/arch/metag/kernel/smp.c
+++ b/arch/metag/kernel/smp.c
@@ -8,6 +8,7 @@
  * published by the Free Software Foundation.
  */
 #include <linux/atomic.h>
+#include <linux/completion.h>
 #include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/spinlock.h>
@@ -62,6 +63,8 @@ static DEFINE_PER_CPU(struct ipi_data, ipi_data) = {
 
 static DEFINE_SPINLOCK(boot_lock);
 
+static DECLARE_COMPLETION(cpu_running);
+
 /*
  * "thread" is assumed to be a valid Meta hardware thread ID.
  */
@@ -235,20 +238,12 @@ int __cpuinit __cpu_up(unsigned int cpu, struct task_struct *idle)
          */
         ret = boot_secondary(thread, idle);
         if (ret == 0) {
-                unsigned long timeout;
-
                 /*
                  * CPU was successfully started, wait for it
                  * to come online or time out.
                  */
-                timeout = jiffies + HZ;
-                while (time_before(jiffies, timeout)) {
-                        if (cpu_online(cpu))
-                                break;
-
-                        udelay(10);
-                        barrier();
-                }
+                wait_for_completion_timeout(&cpu_running,
+                                            msecs_to_jiffies(1000));
 
                 if (!cpu_online(cpu))
                         ret = -EIO;
@@ -391,6 +386,7 @@ asmlinkage void secondary_start_kernel(void)
          * OK, now it's safe to let the boot CPU continue
          */
         set_cpu_online(cpu, true);
+        complete(&cpu_running);
 
         /*
          * Enable local interrupts.