linux-kernel - [PATCH] x86, therm: Only read the initial value of thermal LVT entry on BSP

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Date:	Fri, 6 Nov 2009 13:46:46 +0800
From:	Yong Wang <yong.y.wang@...ux.intel.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	suresh.b.siddha@...el.com, qi.wang@...el.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH] x86, therm: Only read the initial value of thermal LVT
	entry on BSP

Only read the initial value of thermal LVT entry on BSP. The initial
value of thermal LVT entries on all APs always reads 0x10000 because
APs are woken up by BSP issuing INIT-SIPI-SIPI sequence to them and
LVT registers are reset to 0s except for mask bits which are set to
1s when APs receive INIT IPI.

It is enough to check only BSP since BIOS is always setting the same
value for all threads/cores.

Signed-off-by: Yong Wang <yong.y.wang@...el.com>
---
 arch/x86/kernel/cpu/mcheck/therm_throt.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
index b3a1dba..69ba972 100644
--- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
+++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
@@ -259,6 +259,7 @@ void intel_init_thermal(struct cpuinfo_x86 *c)
 	unsigned int cpu = smp_processor_id();
 	int tm2 = 0;
 	u32 l, h;
+	static u32 lvtthmr;
 
 	/* Thermal monitoring depends on ACPI and clock modulation*/
 	if (!cpu_has(c, X86_FEATURE_ACPI) || !cpu_has(c, X86_FEATURE_ACC))
@@ -270,7 +271,19 @@ void intel_init_thermal(struct cpuinfo_x86 *c)
 	 * since it might be delivered via SMI already:
 	 */
 	rdmsr(MSR_IA32_MISC_ENABLE, l, h);
-	h = apic_read(APIC_LVTTHMR);
+
+	/*
+	 * Only read the initial value of thermal LVT entry on BSP. The
+	 * initial value of thermal LVT entries on all APs always reads
+	 * 0x10000 because APs are woken up by BSP issuing INIT-SIPI-SIPI
+	 * sequence to them and LVT registers are reset to 0s except for
+	 * the mask bits which are set to 1s when APs receive INIT IPI.
+	 */
+	if (cpu == 0)
+		lvtthmr = apic_read(APIC_LVTTHMR);
+
+	h = lvtthmr;
+
 	if ((l & MSR_IA32_MISC_ENABLE_TM1) && (h & APIC_DM_SMI)) {
 		printk(KERN_DEBUG
 		       "CPU%d: Thermal monitoring handled by SMI\n", cpu);
--
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