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Commit 14796fca authored by Len Brown's avatar Len Brown
Browse files

intel_idle: disable NHM/WSM HW C-state auto-demotion 

Hardware C-state auto-demotion is a mechanism where the HW overrides
the OS C-state request, instead demoting to a shallower state,
which is less expensive, but saves less power.

Modern Linux should generally get exactly the states it requests.
In particular, when a CPU is taken off-line, it must not be demoted, else
it can prevent the entire package from reaching deep C-states.

https://bugzilla.kernel.org/show_bug.cgi?id=25252



Signed-off-by: default avatarLen Brown <len.brown@intel.com>
parent 100b33c8

arch/x86/include/asm/msr-index.h

+4 −0
Original line number Diff line number Diff line
@@ -36,6 +36,10 @@ 
#define MSR_IA32_PERFCTR1		0x000000c2

#define MSR_FSB_FREQ			0x000000cd



#define MSR_NHM_SNB_PKG_CST_CFG_CTL	0x000000e2

#define NHM_C3_AUTO_DEMOTE		(1UL << 25)

#define NHM_C1_AUTO_DEMOTE		(1UL << 26)



#define MSR_MTRRcap			0x000000fe

#define MSR_IA32_BBL_CR_CTL		0x00000119

drivers/idle/intel_idle.c

+20 −0
Original line number Diff line number Diff line
@@ -62,6 +62,7 @@ 
#include <linux/notifier.h>

#include <linux/cpu.h>

#include <asm/mwait.h>

#include <asm/msr.h>



#define INTEL_IDLE_VERSION "0.4"

#define PREFIX "intel_idle: "
@@ -84,6 +85,12 @@ static int intel_idle(struct cpuidle_device *dev, struct cpuidle_state *state); 


static struct cpuidle_state *cpuidle_state_table;



/*

 * Hardware C-state auto-demotion may not always be optimal.

 * Indicate which enable bits to clear here.

 */

static unsigned long long auto_demotion_disable_flags;



/*

 * Set this flag for states where the HW flushes the TLB for us

 * and so we don't need cross-calls to keep it consistent.
@@ -281,6 +288,15 @@ static struct notifier_block setup_broadcast_notifier = { 
	.notifier_call = setup_broadcast_cpuhp_notify,

};



static void auto_demotion_disable(void *dummy)

{

	unsigned long long msr_bits;



	rdmsrl(MSR_NHM_SNB_PKG_CST_CFG_CTL, msr_bits);

	msr_bits &= ~auto_demotion_disable_flags;

	wrmsrl(MSR_NHM_SNB_PKG_CST_CFG_CTL, msr_bits);

}



/*

 * intel_idle_probe()

 */
@@ -324,6 +340,8 @@ static int intel_idle_probe(void) 
	case 0x25:	/* Westmere */

	case 0x2C:	/* Westmere */

		cpuidle_state_table = nehalem_cstates;

		auto_demotion_disable_flags =

			(NHM_C1_AUTO_DEMOTE | NHM_C3_AUTO_DEMOTE);

		break;



	case 0x1C:	/* 28 - Atom Processor */
@@ -436,6 +454,8 @@ static int intel_idle_cpuidle_devices_init(void) 
			return -EIO;

		}

	}

	if (auto_demotion_disable_flags)

		smp_call_function(auto_demotion_disable, NULL, 1);



	return 0;

}