Commit 5861381d authored Mar 21, 2019 by Rafael J. Wysocki

PM / arch: x86: Rework the MSR_IA32_ENERGY_PERF_BIAS handling



The current handling of MSR_IA32_ENERGY_PERF_BIAS in the kernel is
problematic, because it may cause changes made by user space to that
MSR (with the help of the x86_energy_perf_policy tool, for example)
to be lost every time a CPU goes offline and then back online as well
as during system-wide power management transitions into sleep states
and back into the working state.

The first problem is that if the current EPB value for a CPU going
online is 0 ('performance'), the kernel will change it to 6 ('normal')
regardless of whether or not this is the first bring-up of that CPU.
That also happens during system-wide resume from sleep states
(including, but not limited to, hibernation).  However, the EPB may
have been adjusted by user space this way and the kernel should not
blindly override that setting.

The second problem is that if the platform firmware resets the EPB
values for any CPUs during system-wide resume from a sleep state,
the kernel will not restore their previous EPB values that may
have been set by user space before the preceding system-wide
suspend transition.  Again, that behavior may at least be confusing
from the user space perspective.

In order to address these issues, rework the handling of
MSR_IA32_ENERGY_PERF_BIAS so that the EPB value is saved on CPU
offline and restored on CPU online as well as (for the boot CPU)
during the syscore stages of system-wide suspend and resume
transitions, respectively.

However, retain the policy by which the EPB is set to 6 ('normal')
on the first bring-up of each CPU if its initial value is 0, based
on the observation that 0 may mean 'not initialized' just as well as
'performance' in that case.

While at it, move the MSR_IA32_ENERGY_PERF_BIAS handling code into
a separate file and document it in Documentation/admin-guide.

Fixes: abe48b10 (x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS)
Fixes: b51ef52d (x86/cpu: Restore MSR_IA32_ENERGY_PERF_BIAS after resume)
Reported-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>

parent 8c2ffd91

Documentation/admin-guide/pm/intel_epb.rst

0 → 100644

+6 −0

Original line number	Diff line number	Diff line
		======================================
		Intel Performance and Energy Bias Hint
		======================================

		.. kernel-doc:: arch/x86/kernel/cpu/intel_epb.c
		:doc: overview

Documentation/admin-guide/pm/working-state.rst

+1 −0

Original line number	Diff line number	Diff line
		@@ -8,3 +8,4 @@ Working-State Power Management
		cpuidle
		cpufreq
		intel_pstate
		intel_epb

arch/x86/kernel/cpu/Makefile

+1 −1

Original line number	Diff line number	Diff line
		@@ -28,7 +28,7 @@ obj-y += cpuid-deps.o
		obj-$(CONFIG_PROC_FS) += proc.o
		obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o

		obj-$(CONFIG_CPU_SUP_INTEL) += intel.o intel_pconfig.o
		obj-$(CONFIG_CPU_SUP_INTEL) += intel.o intel_pconfig.o intel_epb.o
		obj-$(CONFIG_CPU_SUP_AMD) += amd.o
		obj-$(CONFIG_CPU_SUP_HYGON) += hygon.o
		obj-$(CONFIG_CPU_SUP_CYRIX_32) += cyrix.o

arch/x86/kernel/cpu/common.c

+0 −17

Original line number	Diff line number	Diff line
		@@ -1864,23 +1864,6 @@ void cpu_init(void)
		}
		#endif

		static void bsp_resume(void)
		{
		if (this_cpu->c_bsp_resume)
		this_cpu->c_bsp_resume(&boot_cpu_data);
		}

		static struct syscore_ops cpu_syscore_ops = {
		.resume = bsp_resume,
		};

		static int __init init_cpu_syscore(void)
		{
		register_syscore_ops(&cpu_syscore_ops);
		return 0;
		}
		core_initcall(init_cpu_syscore);

		/*
		* The microcode loader calls this upon late microcode load to recheck features,
		* only when microcode has been updated. Caller holds microcode_mutex and CPU

arch/x86/kernel/cpu/cpu.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -14,7 +14,6 @@ struct cpu_dev {
		void (c_init)(struct cpuinfo_x86 );
		void (c_identify)(struct cpuinfo_x86 );
		void (c_detect_tlb)(struct cpuinfo_x86 );
		void (c_bsp_resume)(struct cpuinfo_x86 );
		int c_x86_vendor;
		#ifdef CONFIG_X86_32
		/* Optional vendor specific routine to obtain the cache size. */

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