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Commit 0c07ee38 authored by Andi Kleen's avatar Andi Kleen Committed by Ingo Molnar
Browse files

x86: use the correct cpuid method to detect MWAIT support for C states 



Previously there was a AMD specific quirk to handle the case of
AMD Fam10h MWAIT not supporting any C states. But it turns out
that CPUID already has ways to detectly detect that without
using special quirks.

The new code simply checks if MWAIT supports at least C1 and doesn't
use it if it doesn't. No more vendor specific code.

Note this is does not simply clear MWAIT because MWAIT can be still
useful even without C states.

Credit goes to Ben Serebrin for pointing out the (nearly) obvious.

Cc: "Andreas Herrmann" <andreas.herrmann3@amd.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 30d432df

arch/x86/kernel/cpu/amd.c

+0 −3
Original line number Diff line number Diff line
@@ -300,9 +300,6 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c) 
		local_apic_timer_disabled = 1;

#endif



	if (c->x86 == 0x10 && !force_mwait)

		clear_bit(X86_FEATURE_MWAIT, c->x86_capability);



	/* K6s reports MCEs but don't actually have all the MSRs */

	if (c->x86 < 6)

		clear_bit(X86_FEATURE_MCE, c->x86_capability);

arch/x86/kernel/process_32.c

+9 −1
Original line number Diff line number Diff line
@@ -285,9 +285,17 @@ static void mwait_idle(void) 
	mwait_idle_with_hints(0, 0);

}



static int mwait_usable(const struct cpuinfo_x86 *c)

{

	if (force_mwait)

		return 1;

	/* Any C1 states supported? */

	return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0;

}



void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)

{

	if (cpu_has(c, X86_FEATURE_MWAIT)) {

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

		printk("monitor/mwait feature present.\n");

		/*

		 * Skip, if setup has overridden idle.

arch/x86/kernel/process_64.c

+10 −1
Original line number Diff line number Diff line
@@ -280,10 +280,19 @@ static void mwait_idle(void) 
	}

}





static int mwait_usable(const struct cpuinfo_x86 *c)

{

	if (force_mwait)

		return 1;

	/* Any C1 states supported? */

	return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0;

}



void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)

{

	static int printed;

	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

arch/x86/kernel/setup_64.c

+0 −4
Original line number Diff line number Diff line
@@ -761,10 +761,6 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c) 
	/* MFENCE stops RDTSC speculation */

	set_cpu_cap(c, X86_FEATURE_MFENCE_RDTSC);



	/* Family 10 doesn't support C states in MWAIT so don't use it */

	if (c->x86 == 0x10 && !force_mwait)

		clear_cpu_cap(c, X86_FEATURE_MWAIT);



	if (amd_apic_timer_broken())

		disable_apic_timer = 1;

}