x86: disable mwait for AMD family 10H/11H CPUs (e9623b35) · Commits · 戴 / test

The previous revert of left out the mwait disable condition for AMD family 10H/11H CPUs. Andreas Herrman said: It depends on the CPU. For AMD CPUs that support MWAIT this is wrong. Family 0x10 and 0x11 CPUs will enter C1 on HLT. Powersavings then depend on a clock divisor and current Pstate of the core. If all cores of a processor are in halt state (C1) the processor can enter the C1E (C1 enhanced) state. If mwait is used this will never happen. Thus HLT saves more power than MWAIT here. It might be best to switch off the mwait flag for these AMD CPU families like it was introduced with commit (x86: Don't use MWAIT on AMD Family 10) Re-add the AMD families 10H/11H check and disable the mwait usage for those. Signed-off-by:

Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/process.c

+28 −1

Original line number	Diff line number	Diff line
		@@ -110,6 +110,33 @@ static void poll_idle(void)
		cpu_relax();
		}

		/*
		* mwait selection logic:
		*
		* It depends on the CPU. For AMD CPUs that support MWAIT this is
		* wrong. Family 0x10 and 0x11 CPUs will enter C1 on HLT. Powersavings
		* then depend on a clock divisor and current Pstate of the core. If
		* all cores of a processor are in halt state (C1) the processor can
		* enter the C1E (C1 enhanced) state. If mwait is used this will never
		* happen.
		*
		* idle=mwait overrides this decision and forces the usage of mwait.
		*/
		static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
		{
		if (force_mwait)
		return 1;

		if (c->x86_vendor == X86_VENDOR_AMD) {
		switch(c->x86) {
		case 0x10:
		case 0x11:
		return 0;
		}
		}
		return 1;
		}

		void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
		{
		static int selected;
		@@ -122,7 +149,7 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
		" performance may degrade.\n");
		}
		#endif
		if (cpu_has(c, X86_FEATURE_MWAIT)) {
		if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
		/*
		* Skip, if setup has overridden idle.
		* One CPU supports mwait => All CPUs supports mwait

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