[PATCH] ARM: smp: Introduce ARCH_SKIP_SECONDARY_CALIBRATE to

[Santosh Shilimkar]

speed-up boot

On some architectures, secondary cores shares clock with primiary
core and hence scale together. Hence secondary core lpj calibration
is not necessary and can be skipped to save considerable time.

This can speed up the secondary cpu boot and hotplug cpu online
paths.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar at ti.com>
Cc: Russell King <rmk+kernel at arm.linux.org.uk>
---
 arch/arm/Kconfig      |   10 ++++++++++
 arch/arm/kernel/smp.c |   17 ++++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5cff165..677d87f 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1418,6 +1418,16 @@ config ARCH_SPARSEMEM_DEFAULT
 config ARCH_SELECT_MEMORY_MODEL
 	def_bool ARCH_SPARSEMEM_ENABLE

+config ARCH_SKIP_SECONDARY_CALIBRATE
+	bool "Skip secondary CPU calibration"
+	depends on SMP
+	help
+	  On some architectures, secondary cores shares clock with
primiary
+	  core and hence scale together. Hence secondary core lpj
calibration
+	  is not necessary and can be skipped to save considerable time.
+
+	  If unsure, say n.
+
 config HIGHMEM
 	bool "High Memory Support (EXPERIMENTAL)"
 	depends on MMU && EXPERIMENTAL
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 4539ebc..baf2707 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -270,6 +270,20 @@ static void __cpuinit smp_store_cpu_info(unsigned int
cpuid)
 }

 /*
+ * Skip the secondary calibration on architectures sharing clock
+ * with primary cpu. Archs can use ARCH_SKIP_SECONDARY_CALIBRATE
+ * for this.
+ */
+static inline int skip_secondary_calibrate(void)
+{
+#ifdef CONFIG_ARCH_SKIP_SECONDARY_CALIBRATE
+	return 0;
+#else
+	return -ENXIO;
+#endif
+}
+
+/*
  * This is the secondary CPU boot entry.  We're using this CPUs
  * idle thread stack, but a set of temporary page tables.
  */
@@ -312,7 +326,8 @@ asmlinkage void __cpuinit secondary_start_kernel(void)
 	 */
 	percpu_timer_setup();

-	calibrate_delay();
+	if (skip_secondary_calibrate())
+		calibrate_delay();

 	smp_store_cpu_info(cpu);

-- 
1.6.0.4

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