[PATCH] x86/timers: Move simple_udelay_calibration() past kvmclock_init()

From: Boris Ostrovsky
Date: Mon Sep 11 2017 - 11:04:51 EST

simple_udelay_calibration() relies on x86_platform's calibration ops.
For KVM these ops are set late in setup_arch() and so
simple_udelay_calibration() ends up using native version.

Besides being possibly incorrect, this significantly increases kernel
boot time. For example, on my laptop executing start_kernel() by a guest
takes ~10 times more than when KVM's ops are used.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Alternatively, we could start calling simple_udelay_calibration() only
on bare metal: My understanding is that the only reason it exists is to
help with USB3 earlyprink driver, which I don't think is useful to guests

arch/x86/kernel/setup.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index f81823695014..749439fba076 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1039,8 +1039,6 @@ void __init setup_arch(char **cmdline_p)

- simple_udelay_calibration();

/* after parse_early_param, so could debug it */
@@ -1221,6 +1219,8 @@ void __init setup_arch(char **cmdline_p)

+ simple_udelay_calibration();