arch/tile: add "nop" after "nap" to help GX idle power draw

This avoids the hardware istream prefetcher doing unnecessary work.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

diff --git a/arch/tile/kernel/entry.S b/arch/tile/kernel/entry.S
index 431e9ae..ec91568 100644 (file)
--- a/arch/tile/kernel/entry.S
+++ b/arch/tile/kernel/entry.S
@@ -85,6 +85,7 @@ STD_ENTRY(cpu_idle_on_new_stack)
 /* Loop forever on a nap during SMP boot. */
 STD_ENTRY(smp_nap)
        nap
+       nop       /* avoid provoking the icache prefetch with a jump */
        j smp_nap /* we are not architecturally guaranteed not to exit nap */
        jrp lr    /* clue in the backtracer */
        STD_ENDPROC(smp_nap)
@@ -105,5 +106,6 @@ STD_ENTRY(_cpu_idle)
        .global _cpu_idle_nap
 _cpu_idle_nap:
        nap
+       nop       /* avoid provoking the icache prefetch with a jump */
        jrp lr
        STD_ENDPROC(_cpu_idle)

diff --git a/arch/tile/kernel/smp.c b/arch/tile/kernel/smp.c
index a44e103..7b6df8c 100644 (file)
--- a/arch/tile/kernel/smp.c
+++ b/arch/tile/kernel/smp.c
@@ -103,7 +103,7 @@ static void smp_stop_cpu_interrupt(void)
        set_cpu_online(smp_processor_id(), 0);
        arch_local_irq_disable_all();
        for (;;)
-               asm("nap");
+               asm("nap; nop");
 }
 
 /* This function calls the 'stop' function on all other CPUs in the system. */