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

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This avoids the hardware istream prefetcher doing unnecessary work.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
This commit is contained in:
Chris Metcalf 2012-03-29 15:57:18 -04:00
parent bfffe79bc2
commit 8c92ba6c32
2 changed files with 3 additions and 1 deletions
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2
arch/tile/kernel/entry.S
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@ -85,6 +85,7 @@ STD_ENTRY(cpu_idle_on_new_stack)
/* Loop forever on a nap during SMP boot. */ /* Loop forever on a nap during SMP boot. */
STD_ENTRY(smp_nap) STD_ENTRY(smp_nap)
nap nap
nop /* avoid provoking the icache prefetch with a jump */
j smp_nap /* we are not architecturally guaranteed not to exit nap */ j smp_nap /* we are not architecturally guaranteed not to exit nap */
jrp lr /* clue in the backtracer */ jrp lr /* clue in the backtracer */
STD_ENDPROC(smp_nap) STD_ENDPROC(smp_nap)
@ -105,5 +106,6 @@ STD_ENTRY(_cpu_idle)
.global _cpu_idle_nap .global _cpu_idle_nap
_cpu_idle_nap: _cpu_idle_nap:
nap nap
nop /* avoid provoking the icache prefetch with a jump */
jrp lr jrp lr
STD_ENDPROC(_cpu_idle) STD_ENDPROC(_cpu_idle)

2
arch/tile/kernel/smp.c
View file

@ -103,7 +103,7 @@ static void smp_stop_cpu_interrupt(void)
set_cpu_online(smp_processor_id(), 0); set_cpu_online(smp_processor_id(), 0);
arch_local_irq_disable_all(); arch_local_irq_disable_all();
for (;;) for (;;)
asm("nap"); asm("nap; nop");
} }
/* This function calls the 'stop' function on all other CPUs in the system. */ /* This function calls the 'stop' function on all other CPUs in the system. */