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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: Len Brown <len.brown@intel.com>
This commit is contained in:
Len Brown 2011-01-18 20:48:27 -05:00
parent 100b33c8bd
commit 14796fca2b
2 changed files with 24 additions and 0 deletions
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4
arch/x86/include/asm/msr-index.h
View File

@ -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

20
drivers/idle/intel_idle.c
View File

@ -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;
}