From e736ad548db152776de61d7a26805cfae77ce5ce Mon Sep 17 00:00:00 2001
From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
Date: Fri, 6 Feb 2009 16:52:05 -0800
Subject: [PATCH] x86: add clflush before monitor for Intel 7400 series
For Intel 7400 series CPUs, the recommendation is to use a clflush on the
monitored address just before monitor and mwait pair [1].
This clflush makes sure that there are no false wakeups from mwait when the
monitored address was recently written to.
[1] "MONITOR/MWAIT Recommendations for Intel Xeon Processor 7400 series"
section in specification update document of 7400 series
http://download.intel.com/design/xeon/specupdt/32033601.pdf
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/include/asm/cpufeature.h | 1 +
arch/x86/kernel/cpu/intel.c | 3 +++
arch/x86/kernel/process.c | 6 ++++++
3 files changed, 10 insertions(+)
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index ea408dcba5135..7301e60dc4a83 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -93,6 +93,7 @@
#define X86_FEATURE_XTOPOLOGY (3*32+22) /* cpu topology enum extensions */
#define X86_FEATURE_TSC_RELIABLE (3*32+23) /* TSC is known to be reliable */
#define X86_FEATURE_NONSTOP_TSC (3*32+24) /* TSC does not stop in C states */
+#define X86_FEATURE_CLFLUSH_MONITOR (3*32+25) /* "" clflush reqd with monitor */
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 (4*32+ 0) /* "pni" SSE-3 */
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 430e5c38a5449..24ff26a38adec 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -291,6 +291,9 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
ds_init_intel(c);
}
+ if (c->x86 == 6 && c->x86_model == 29 && cpu_has_clflush)
+ set_cpu_cap(c, X86_FEATURE_CLFLUSH_MONITOR);
+
#ifdef CONFIG_X86_64
if (c->x86 == 15)
c->x86_cache_alignment = c->x86_clflush_size * 2;
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index e68bb9e30864e..6d12f7e37f8c1 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -180,6 +180,9 @@ void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
trace_power_start(&it, POWER_CSTATE, (ax>>4)+1);
if (!need_resched()) {
+ if (cpu_has(¤t_cpu_data, X86_FEATURE_CLFLUSH_MONITOR))
+ clflush((void *)¤t_thread_info()->flags);
+
__monitor((void *)¤t_thread_info()->flags, 0, 0);
smp_mb();
if (!need_resched())
@@ -194,6 +197,9 @@ static void mwait_idle(void)
struct power_trace it;
if (!need_resched()) {
trace_power_start(&it, POWER_CSTATE, 1);
+ if (cpu_has(¤t_cpu_data, X86_FEATURE_CLFLUSH_MONITOR))
+ clflush((void *)¤t_thread_info()->flags);
+
__monitor((void *)¤t_thread_info()->flags, 0, 0);
smp_mb();
if (!need_resched())
--
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