linux-kernel - [tip:x86/mrst] x86: Avoid check hlt for newer cpus

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Message-ID: <tip-d081dd5fe0ed8449433b972d3080f9d776e9424b@git.kernel.org>
Date:	Fri, 7 May 2010 22:18:46 GMT
From:	tip-bot for Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	tglx@...utronix.de, jacob.jun.pan@...ux.intel.com
Subject: [tip:x86/mrst] x86: Avoid check hlt for newer cpus

Commit-ID:  d081dd5fe0ed8449433b972d3080f9d776e9424b
Gitweb:     http://git.kernel.org/tip/d081dd5fe0ed8449433b972d3080f9d776e9424b
Author:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
AuthorDate: Fri, 7 May 2010 14:59:45 -0700
Committer:  H. Peter Anvin <hpa@...or.com>
CommitDate: Fri, 7 May 2010 15:15:47 -0700

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).

[ hpa: corrected family > 5 to family >= 5 ]

Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
LKML-Reference: <1273269585-14346-1-git-send-email-jacob.jun.pan@...ux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@...or.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..38f20e8 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 (boot_cpu_data >= 5 || paravirt_enabled())
 		return;
 
 	printk(KERN_INFO "Checking 'hlt' instruction... ");
--
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