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Subject[PATCH] smpboot: reuse timer calibration
Date
From: Arjan van de Ven <arjan@linux.intel.com>
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@molgen.mpg.de>
---

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
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