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>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 1fa091e05690..32b25bcaf865 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -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: "
@@ -85,6 +86,12 @@ 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.
  * If this flag is set, SW flushes the TLB, so even if the
@@ -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;
 }