linux-kernel - [PATCH] x86: Make mwait_usable() respect "idle=nomwait" kernel parameter

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Message-ID: <20120402140645.6283.21190.stgit@srivatsabhat.in.ibm.com>
Date:	Mon, 02 Apr 2012 19:36:45 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	lenb@...nel.org
Cc:	venki@...gle.com, suresh.b.siddha@...el.com, bp@...64.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, ben@...adent.org.uk, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	deepthi@...ux.vnet.ibm.com
Subject: [PATCH] x86: Make mwait_usable() respect "idle=nomwait" kernel
 parameter

mwait_usable() returns 1 even if the "idle=nomwait" kernel parameter is passed.
Fix it by adding a check for boot_option_idle_override == IDLE_NOMWAIT and
returning 0 if it is set.

Before applying the patch (dmesg snippet):
[    0.000000] Command line: [...] idle=nomwait
[    0.000000] Kernel command line: [...] idle=nomwait
[    0.000000]  RCU dyntick-idle grace-period acceleration is enabled.
[    0.140606] using mwait in idle threads.         <======= mwait being used
[    4.303986] cpuidle: using governor ladder
[    4.308232] cpuidle: using governor menu

After applying the patch:
[    0.000000] Command line: [...] idle=nomwait
[    0.000000] Kernel command line: [...] idle=nomwait
[    0.000000]  RCU dyntick-idle grace-period acceleration is enabled.
[    4.264100] cpuidle: using governor ladder
[    4.268342] cpuidle: using governor menu

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 arch/x86/kernel/process.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index a33afaa..945fbf0 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -621,6 +621,9 @@ int mwait_usable(const struct cpuinfo_x86 *c)
 	if (boot_option_idle_override == IDLE_FORCE_MWAIT)
 		return 1;
 
+	if (boot_option_idle_override == IDLE_NOMWAIT)
+		return 0;
+
 	if (c->cpuid_level < MWAIT_INFO)
 		return 0;
 

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