linux-kernel - [PATCH] x86: avoid check hlt for newer cpus

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Date:	Fri,  7 May 2010 14:59:45 -0700
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Alek Du <alek.du@...el.com>
Cc:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: [PATCH] x86: avoid check hlt for newer cpus

Check hlt instruction was targeted for some older CPUs. It is an expensive
operation in that it takes 4 ticks to break out the check.  We can avoid
such check completely for newer x86 cpus ( family > 5).
http://lkml.org/lkml/2010/5/7/395

Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
---
 arch/x86/kernel/cpu/bugs.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 01a2652..36d9bcf 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -86,7 +86,7 @@ static void __init check_fpu(void)
 
 static void __init check_hlt(void)
 {
-	if (paravirt_enabled())
+	if (paravirt_enabled() || boot_cpu_data.x86 > 5)
 		return;
 
 	printk(KERN_INFO "Checking 'hlt' instruction... ");
-- 
1.6.3.3

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