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Commit 69fb3676 authored by Len Brown's avatar Len Brown
Browse files

x86 idle: remove mwait_idle() and "idle=mwait" cmdline param 



mwait_idle() is a C1-only idle loop intended to be more efficient
than HLT, starting on Pentium-4 HT-enabled processors.

But mwait_idle() has been replaced by the more general
mwait_idle_with_hints(), which handles both C1 and deeper C-states.
ACPI processor_idle and intel_idle use only mwait_idle_with_hints(),
and no longer use mwait_idle().

Here we simplify the x86 native idle code by removing mwait_idle(),
and the "idle=mwait" bootparam used to invoke it.

Since Linux 3.0 there has been a boot-time warning when "idle=mwait"
was invoked saying it would be removed in 2012.  This removal
was also noted in the (now removed:-) feature-removal-schedule.txt.

After this change, kernels configured with
(CONFIG_ACPI=n && CONFIG_INTEL_IDLE=n) when run on hardware
that supports MWAIT will simply use HLT.  If MWAIT is desired
on those systems, cpuidle and the cpuidle drivers above
can be enabled.

Signed-off-by: default avatarLen Brown <len.brown@intel.com>
Cc: x86@kernel.org
parent 6a377ddc

Documentation/kernel-parameters.txt

+1 −6
Original line number Diff line number Diff line
@@ -1039,16 +1039,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			Claim all unknown PCI IDE storage controllers.



	idle=		[X86]

			Format: idle=poll, idle=mwait, idle=halt, idle=nomwait

			Format: idle=poll, idle=halt, idle=nomwait

			Poll forces a polling idle loop that can slightly

			improve the performance of waking up a idle CPU, but

			will use a lot of power and make the system run hot.

			Not recommended.

			idle=mwait: On systems which support MONITOR/MWAIT but

			the kernel chose to not use it because it doesn't save

			as much power as a normal idle loop, use the

			MONITOR/MWAIT idle loop anyways. Performance should be

			the same as idle=poll.

			idle=halt: Halt is forced to be used for CPU idle.

			In such case C2/C3 won't be used again.

			idle=nomwait: Disable mwait for CPU C-states

arch/x86/include/asm/processor.h

+1 −1
Original line number Diff line number Diff line
@@ -725,7 +725,7 @@ extern unsigned long boot_option_idle_override; 
extern bool			amd_e400_c1e_detected;



enum idle_boot_override {IDLE_NO_OVERRIDE=0, IDLE_HALT, IDLE_NOMWAIT,

			 IDLE_POLL, IDLE_FORCE_MWAIT};

			 IDLE_POLL};



extern void enable_sep_cpu(void);

extern int sysenter_setup(void);

arch/x86/kernel/process.c

+1 −78
Original line number Diff line number Diff line
@@ -421,27 +421,6 @@ void stop_this_cpu(void *dummy) 
	}

}



/* Default MONITOR/MWAIT with no hints, used for default C1 state */

static void mwait_idle(void)

{

	if (!need_resched()) {

		trace_power_start_rcuidle(POWER_CSTATE, 1, smp_processor_id());

		trace_cpu_idle_rcuidle(1, smp_processor_id());

		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))

			clflush((void *)&current_thread_info()->flags);



		__monitor((void *)&current_thread_info()->flags, 0, 0);

		smp_mb();

		if (!need_resched())

			__sti_mwait(0, 0);

		else

			local_irq_enable();

		trace_power_end_rcuidle(smp_processor_id());

		trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());

	} else

		local_irq_enable();

}



/*

 * On SMP it's slightly faster (but much more power-consuming!)

 * to poll the ->work.need_resched flag instead of waiting for the
@@ -458,53 +437,6 @@ static void poll_idle(void) 
	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());

}



/*

 * 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.

 */



#define MWAIT_INFO			0x05

#define MWAIT_ECX_EXTENDED_INFO		0x01

#define MWAIT_EDX_C1			0xf0



int mwait_usable(const struct cpuinfo_x86 *c)

{

	u32 eax, ebx, ecx, edx;



	/* Use mwait if idle=mwait boot option is given */

	if (boot_option_idle_override == IDLE_FORCE_MWAIT)

		return 1;



	/*

	 * Any idle= boot option other than idle=mwait means that we must not

	 * use mwait. Eg: idle=halt or idle=poll or idle=nomwait

	 */

	if (boot_option_idle_override != IDLE_NO_OVERRIDE)

		return 0;



	if (c->cpuid_level < MWAIT_INFO)

		return 0;



	cpuid(MWAIT_INFO, &eax, &ebx, &ecx, &edx);

	/* Check, whether EDX has extended info about MWAIT */

	if (!(ecx & MWAIT_ECX_EXTENDED_INFO))

		return 1;



	/*

	 * edx enumeratios MONITOR/MWAIT extensions. Check, whether

	 * C1  supports MWAIT

	 */

	return (edx & MWAIT_EDX_C1);

}



bool amd_e400_c1e_detected;

EXPORT_SYMBOL(amd_e400_c1e_detected);
@@ -576,13 +508,7 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c) 
	if (pm_idle)

		return;



	if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {

		/*

		 * One CPU supports mwait => All CPUs supports mwait

		 */

		pr_info("using mwait in idle threads\n");

		pm_idle = mwait_idle;

	} else if (cpu_has_amd_erratum(amd_erratum_400)) {

	if (cpu_has_amd_erratum(amd_erratum_400)) {

		/* E400: APIC timer interrupt does not wake up CPU from C1e */

		pr_info("using AMD E400 aware idle routine\n");

		pm_idle = amd_e400_idle;
@@ -606,9 +532,6 @@ static int __init idle_setup(char *str) 
		pr_info("using polling idle threads\n");

		pm_idle = poll_idle;

		boot_option_idle_override = IDLE_POLL;

	} else if (!strcmp(str, "mwait")) {

		boot_option_idle_override = IDLE_FORCE_MWAIT;

		WARN_ONCE(1, "\"idle=mwait\" will be removed in 2012\n");

	} else if (!strcmp(str, "halt")) {

		/*

		 * When the boot option of idle=halt is added, halt is

arch/x86/kernel/smpboot.c

+1 −1
Original line number Diff line number Diff line
@@ -1369,7 +1369,7 @@ static inline void mwait_play_dead(void) 
	void *mwait_ptr;

	struct cpuinfo_x86 *c = __this_cpu_ptr(&cpu_info);



	if (!(this_cpu_has(X86_FEATURE_MWAIT) && mwait_usable(c)))

	if (!this_cpu_has(X86_FEATURE_MWAIT))

		return;

	if (!this_cpu_has(X86_FEATURE_CLFLSH))

		return;

drivers/acpi/processor_idle.c

+0 −1
Original line number Diff line number Diff line
@@ -84,7 +84,6 @@ static DEFINE_PER_CPU(struct cpuidle_device *, acpi_cpuidle_device); 
static int disabled_by_idle_boot_param(void)

{

	return boot_option_idle_override == IDLE_POLL ||

		boot_option_idle_override == IDLE_FORCE_MWAIT ||

		boot_option_idle_override == IDLE_HALT;

}