powerpc: Don't spin on sync instruction at boot time

Push the sync below the secondary smp init hold loop and comment its purpose.
This should speed up boot by reducing global traffic during the single-threaded
portion of boot.

Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index ecced1eb03ae4f83d56c555ad8b6642b7292f34b..cc8fb474d5204ed3c2cf2c48bd754b1fdf3758c9 100644 (file)
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -1198,7 +1198,6 @@ _GLOBAL(generic_secondary_smp_init)
 3:     HMT_LOW
        lbz     r23,PACAPROCSTART(r13)  /* Test if this processor should */
                                        /* start.                        */
-       sync
 
 #ifndef CONFIG_SMP
        b       3b                      /* Never go on non-SMP           */
@@ -1206,6 +1205,8 @@ _GLOBAL(generic_secondary_smp_init)
        cmpwi   0,r23,0
        beq     3b                      /* Loop until told to go         */
 
+       sync                            /* order paca.run and cur_cpu_spec */
+
        /* See if we need to call a cpu state restore handler */
        LOAD_REG_IMMEDIATE(r23, cur_cpu_spec)
        ld      r23,0(r23)