Patch "cpufreq: intel_pstate: Disable energy efficiency optimization" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

cpufreq: intel_pstate: Disable energy efficiency optimization

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
cpufreq-intel_pstate-disable-energy-efficiency-optimization.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Srinivas Pandruvada <[email protected]>
Date: Fri, 3 Feb 2017 14:18:39 -0800
Subject: cpufreq: intel_pstate: Disable energy efficiency optimization

From: Srinivas Pandruvada <[email protected]>

commit 6e978b22efa1db9f6e71b24440b5f1d93e968ee3 upstream.

Some Kabylake desktop processors may not reach max turbo when running in HWP mode, even if running under sustained 100% utilization.

This occurs when the HWP.EPP (Energy Performance Preference) is set to "balance_power" (0x80) -- the default on most systems.

It occurs because the platform BIOS may erroneously enable an energy-efficiency setting -- MSR_IA32_POWER_CTL BIT-EE, which is not recommended to be enabled on this SKU.

On the failing systems, this BIOS issue was not discovered when the desktop motherboard was tested with Windows, because the BIOS also neglects to provide the ACPI/CPPC table, that Windows requires to enable HWP, and so Windows runs in legacy P-state mode, where this setting has no effect.

Linux' intel_pstate driver does not require ACPI/CPPC to enable HWP, and so it runs in HWP mode, exposing this incorrect BIOS configuration.

There are several ways to address this problem.

First, Linux can also run in legacy P-state mode on this system. As intel_pstate is how Linux enables HWP, booting with "intel_pstate=disable"
will run in acpi-cpufreq/ondemand legacy p-state mode.

Or second, the "performance" governor can be used with intel_pstate, which will modify HWP.EPP to 0.

Or third, starting in 4.10, the /sys/devices/system/cpu/cpufreq/policy*/energy_performance_preference attribute in can be updated from "balance_power" to "performance".

Or fourth, apply this patch, which fixes the erroneous setting of MSR_IA32_POWER_CTL BIT_EE on this model, allowing the default configuration to function as designed.

---
 drivers/cpufreq/intel_pstate.c |   30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

@@ -820,6 +820,25 @@ static void intel_pstate_hwp_enable(stru
 	wrmsrl_on_cpu(cpudata->cpu, MSR_PM_ENABLE, 0x1);
 }
 
+#define MSR_IA32_POWER_CTL_BIT_EE	19
+
+/* Disable energy efficiency optimization */
+static void intel_pstate_disable_ee(int cpu)
+{
+	u64 power_ctl;
+	int ret;
+
+	ret = rdmsrl_on_cpu(cpu, MSR_IA32_POWER_CTL, &power_ctl);
+	if (ret)
+		return;
+
+	if (!(power_ctl & BIT(MSR_IA32_POWER_CTL_BIT_EE))) {
+		pr_info("Disabling energy efficiency optimization\n");
+		power_ctl |= BIT(MSR_IA32_POWER_CTL_BIT_EE);
+		wrmsrl_on_cpu(cpu, MSR_IA32_POWER_CTL, power_ctl);
+	}
+}
+
 static int atom_get_min_pstate(void)
 {
 	u64 value;

@@ -1420,6 +1439,11 @@ static const struct x86_cpu_id intel_pst
 	{}
 };
 
+static const struct x86_cpu_id intel_pstate_cpu_ee_disable_ids[] = {
+	ICPU(INTEL_FAM6_KABYLAKE_DESKTOP, core_params),
+	{}
+};
+
 static int intel_pstate_init_cpu(unsigned int cpunum)
 {
 	struct cpudata *cpu;

@@ -1435,6 +1459,12 @@ static int intel_pstate_init_cpu(unsigne
 	cpu->cpu = cpunum;
 
 	if (hwp_active) {
+		const struct x86_cpu_id *id;
+
+		id = x86_match_cpu(intel_pstate_cpu_ee_disable_ids);
+		if (id)
+			intel_pstate_disable_ee(cpunum);
+
 		intel_pstate_hwp_enable(cpu);
 		pid_params.sample_rate_ms = 50;
 		pid_params.sample_rate_ns = 50 * NSEC_PER_MSEC;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/cpufreq-intel_pstate-disable-energy-efficiency-optimization.patch