[PATCH] smpboot: reuse timer calibration

[Paul Menzel]

From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Date: Wed, 11 Feb 2015 17:28:14 -0600

NO point recalibrating for known-constant tsc ...
saves 200ms+ of boot time.

Signed-off-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx>
---

Arjan, can your Signed-off-by line be added? On what device, did you 
test this?

This upstreams the patch from Clear Linux.

https://github.com/clearlinux-pkgs/linux/blob/master/0108-smpboot-reuse-timer-calibration.patch

 arch/x86/kernel/tsc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index c59454c382fd..42b07ed467d2 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1525,6 +1525,9 @@ unsigned long calibrate_delay_is_known(void)
 	if (!constant_tsc || !mask)
 		return 0;

+	if (cpu != 0)
+		return cpu_data(0).loops_per_jiffy;
+
 	sibling = cpumask_any_but(mask, cpu);
 	if (sibling < nr_cpu_ids)
 		return cpu_data(sibling).loops_per_jiffy;
--
2.24.0.rc1