linux-kernel - [PATCH 1/3] x86/vmware: Use tsc_khz value for calibrate

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Date:   Tue, 25 Oct 2016 22:20:36 -0700
From:   Alexey Makhalov <amakhalov@...are.com>
To:     <corbet@....net>, <akataria@...are.com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <hpa@...or.com>, <x86@...nel.org>
CC:     <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>,
        <monitor-list@...are.com>, <pv-drivers@...are.com>,
        <time-lords@...are.com>, Alexey Makhalov <amakhalov@...are.com>
Subject: [PATCH 1/3] x86/vmware: Use tsc_khz value for calibrate_cpu()

After aa297292d708, there are separate native calibrations for cpu_khz and
tsc_khz. The code sets x86_platform.calibrate_cpu to native_calibrate_cpu()
which looks in cpuid leaf 0x16 or msrs for the cpu frequency. Since we keep
the tsc_khz constant (even after vmotion), the cpu_khz and tsc_khz may
start diverging.

tsc_init() now does

	cpu_khz = x86_platform.calibrate_cpu();
	tsc_khz = x86_platform.calibrate_tsc();
	if (tsc_khz == 0)
		tsc_khz = cpu_khz;
	else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz)
		cpu_khz = tsc_khz;

We want the cpu_khz and tsc_khz to be sync even if they diverge less then
10%.
This patch resolves this issue by setting x86_platform.calibrate_cpu to
vmware_get_tsc_khz().

Signed-off-by: Alexey Makhalov <amakhalov@...are.com>
Acked-by: Alok N Kataria <akataria@...are.com>
---
 arch/x86/kernel/cpu/vmware.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index 4e34da4b..480790f 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -83,6 +83,7 @@ static void __init vmware_platform_setup(void)
 
 		vmware_tsc_khz = tsc_khz;
 		x86_platform.calibrate_tsc = vmware_get_tsc_khz;
+		x86_platform.calibrate_cpu = vmware_get_tsc_khz;
 
 #ifdef CONFIG_X86_LOCAL_APIC
 		/* Skip lapic calibration since we know the bus frequency. */
-- 
2.10.1