Two x86 idle cleanups

Two x86 idle cleanups

[Len Brown]

The following two patches remove cruft from the x86 native idle code.
These two removals have been marked with a WARN() since Linux 3.0.

Let me know if you see any troubles w/ these patches.

TIP,
These will conflict with another patch in my tree.
So if you approve, please Ack and I can carry in my tree.

thanks,
Len Brown, Intel Open Source Technology Center

[PATCH 1/2] x86 idle: remove mwait_idle() and "idle=mwait" cmdline param

[Len Brown]

From: Len Brown <len.brown@intel.com>

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But mwait_idle() has been replaced by the more general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: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org
---
 Documentation/kernel-parameters.txt |  7 +---
 arch/x86/include/asm/processor.h    |  2 +-
 arch/x86/kernel/process.c           | 79 +------------------------------------
 arch/x86/kernel/smpboot.c           |  2 +-
 drivers/acpi/processor_idle.c       |  1 -
 5 files changed, 4 insertions(+), 87 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 363e348..3b0cd1e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -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
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index c2f7f47..8a28fea 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -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);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7ed9f6b0..cd5a4c9 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -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
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ed0fe38..a6ceaed 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -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;
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index ed9a1cc..52a5e3a 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -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;
 }
 
-- 
1.8.1.3.535.ga923c31

[PATCH 2/2] x86 idle: remove 32-bit-only "no-hlt" parameter, hlt_works_ok flag

[Len Brown]

From: Len Brown <len.brown@intel.com>

Remove 32-bit x86 a cmdline param "no-hlt",
and the cpuinfo_x86.hlt_works_ok that it sets.

If a user wants to avoid HLT, then "idle=poll"
is much more useful, as it avoids invocation of HLT
in idle, while "no-hlt" failed to do so.

Indeed, hlt_works_ok was consulted in only 2 places.

First, in /proc/cpuinfo where "hlt_bug yes"
would be printed if and only if the user booted
the system with "no-hlt" -- as there was no other code
to set that flag.

Second, it was consulted in stop_this_cpu(), which is invoked
by native_machine_halt()/reboot_interrupt()/smp_stop_nmi_callback() --
all cases where the machine is being shutdown/reset.
The flag was not consulted in the more frequently invoked
play_dead()/hlt_play_dead() used in processor offline and suspend.

Since Linux-3.0 there has been a run-time notice upon "no-hlt" invocations
indicating that it would be removed in 2012.

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org
---
 Documentation/kernel-parameters.txt |  4 ----
 arch/x86/include/asm/processor.h    | 10 ----------
 arch/x86/kernel/cpu/bugs.c          |  9 ---------
 arch/x86/kernel/cpu/proc.c          |  2 --
 arch/x86/kernel/process.c           |  6 ++----
 arch/x86/xen/setup.c                |  3 ---
 6 files changed, 2 insertions(+), 32 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 3b0cd1e..109ee45 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1881,10 +1881,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			wfi(ARM) instruction doesn't work correctly and not to
 			use it. This is also useful when using JTAG debugger.
 
-	no-hlt		[BUGS=X86-32] Tells the kernel that the hlt
-			instruction doesn't work correctly and not to
-			use it.
-
 	no_file_caps	Tells the kernel not to honor file capabilities.  The
 			only way then for a file to be executed with privilege
 			is to be setuid root or executed by root.
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 8a28fea..b9e7d27 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -89,7 +89,6 @@ struct cpuinfo_x86 {
 	char			wp_works_ok;	/* It doesn't on 386's */
 
 	/* Problems on some 486Dx4's and old 386's: */
-	char			hlt_works_ok;
 	char			hard_math;
 	char			rfu;
 	char			fdiv_bug;
@@ -165,15 +164,6 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);
 
 extern const struct seq_operations cpuinfo_op;
 
-static inline int hlt_works(int cpu)
-{
-#ifdef CONFIG_X86_32
-	return cpu_data(cpu).hlt_works_ok;
-#else
-	return 1;
-#endif
-}
-
 #define cache_line_size()	(boot_cpu_data.x86_cache_alignment)
 
 extern void cpu_detect(struct cpuinfo_x86 *c);
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 92dfec9..2488be6 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -17,15 +17,6 @@
 #include <asm/paravirt.h>
 #include <asm/alternative.h>
 
-static int __init no_halt(char *s)
-{
-	WARN_ONCE(1, "\"no-hlt\" is deprecated, please use \"idle=poll\"\n");
-	boot_cpu_data.hlt_works_ok = 0;
-	return 1;
-}
-
-__setup("no-hlt", no_halt);
-
 static int __init no_387(char *s)
 {
 	boot_cpu_data.hard_math = 0;
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 3286a92..e280253 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -28,7 +28,6 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
 {
 	seq_printf(m,
 		   "fdiv_bug\t: %s\n"
-		   "hlt_bug\t\t: %s\n"
 		   "f00f_bug\t: %s\n"
 		   "coma_bug\t: %s\n"
 		   "fpu\t\t: %s\n"
@@ -36,7 +35,6 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
 		   "cpuid level\t: %d\n"
 		   "wp\t\t: %s\n",
 		   c->fdiv_bug ? "yes" : "no",
-		   c->hlt_works_ok ? "no" : "yes",
 		   c->f00f_bug ? "yes" : "no",
 		   c->coma_bug ? "yes" : "no",
 		   c->hard_math ? "yes" : "no",
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index cd5a4c9..aef852e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -415,10 +415,8 @@ void stop_this_cpu(void *dummy)
 	set_cpu_online(smp_processor_id(), false);
 	disable_local_APIC();
 
-	for (;;) {
-		if (hlt_works(smp_processor_id()))
-			halt();
-	}
+	for (;;)
+		halt();
 }
 
 /*
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 2b73b5c..94eac5c 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -556,9 +556,6 @@ void __init xen_arch_setup(void)
 	       COMMAND_LINE_SIZE : MAX_GUEST_CMDLINE);
 
 	/* Set up idle, making sure it calls safe_halt() pvop */
-#ifdef CONFIG_X86_32
-	boot_cpu_data.hlt_works_ok = 1;
-#endif
 	disable_cpuidle();
 	disable_cpufreq();
 	WARN_ON(xen_set_default_idle());
-- 
1.8.1.3.535.ga923c31

[PATCH 2/2 v2] x86 idle: remove 32-bit-only "no-hlt" parameter, hlt_works_ok flag

[Len Brown]

From: Len Brown <len.brown@intel.com>

Remove 32-bit x86 a cmdline param "no-hlt",
and the cpuinfo_x86.hlt_works_ok that it sets.

If a user wants to avoid HLT, then "idle=poll"
is much more useful, as it avoids invocation of HLT
in idle, while "no-hlt" failed to do so.

Indeed, hlt_works_ok was consulted in only 3 places.

First, in /proc/cpuinfo where "hlt_bug yes"
would be printed if and only if the user booted
the system with "no-hlt" -- as there was no other code
to set that flag.

Second, check_hlt() would not invoke halt() if "no-hlt"
were on the cmdline.

Third, it was consulted in stop_this_cpu(), which is invoked
by native_machine_halt()/reboot_interrupt()/smp_stop_nmi_callback() --
all cases where the machine is being shutdown/reset.
The flag was not consulted in the more frequently invoked
play_dead()/hlt_play_dead() used in processor offline and suspend.

Since Linux-3.0 there has been a run-time notice upon "no-hlt" invocations
indicating that it would be removed in 2012.

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org
---
v2: remove also check_hlt()
---
 Documentation/kernel-parameters.txt |  4 ----
 arch/x86/include/asm/processor.h    | 10 ----------
 arch/x86/kernel/cpu/bugs.c          | 27 ---------------------------
 arch/x86/kernel/cpu/proc.c          |  2 --
 arch/x86/kernel/process.c           |  6 ++----
 arch/x86/xen/setup.c                |  3 ---
 6 files changed, 2 insertions(+), 50 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 3b0cd1e..109ee45 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1881,10 +1881,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			wfi(ARM) instruction doesn't work correctly and not to
 			use it. This is also useful when using JTAG debugger.
 
-	no-hlt		[BUGS=X86-32] Tells the kernel that the hlt
-			instruction doesn't work correctly and not to
-			use it.
-
 	no_file_caps	Tells the kernel not to honor file capabilities.  The
 			only way then for a file to be executed with privilege
 			is to be setuid root or executed by root.
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 8a28fea..b9e7d27 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -89,7 +89,6 @@ struct cpuinfo_x86 {
 	char			wp_works_ok;	/* It doesn't on 386's */
 
 	/* Problems on some 486Dx4's and old 386's: */
-	char			hlt_works_ok;
 	char			hard_math;
 	char			rfu;
 	char			fdiv_bug;
@@ -165,15 +164,6 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);
 
 extern const struct seq_operations cpuinfo_op;
 
-static inline int hlt_works(int cpu)
-{
-#ifdef CONFIG_X86_32
-	return cpu_data(cpu).hlt_works_ok;
-#else
-	return 1;
-#endif
-}
-
 #define cache_line_size()	(boot_cpu_data.x86_cache_alignment)
 
 extern void cpu_detect(struct cpuinfo_x86 *c);
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 92dfec9..af6455e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -17,15 +17,6 @@
 #include <asm/paravirt.h>
 #include <asm/alternative.h>
 
-static int __init no_halt(char *s)
-{
-	WARN_ONCE(1, "\"no-hlt\" is deprecated, please use \"idle=poll\"\n");
-	boot_cpu_data.hlt_works_ok = 0;
-	return 1;
-}
-
-__setup("no-hlt", no_halt);
-
 static int __init no_387(char *s)
 {
 	boot_cpu_data.hard_math = 0;
@@ -89,23 +80,6 @@ static void __init check_fpu(void)
 		pr_warn("Hmm, FPU with FDIV bug\n");
 }
 
-static void __init check_hlt(void)
-{
-	if (boot_cpu_data.x86 >= 5 || paravirt_enabled())
-		return;
-
-	pr_info("Checking 'hlt' instruction... ");
-	if (!boot_cpu_data.hlt_works_ok) {
-		pr_cont("disabled\n");
-		return;
-	}
-	halt();
-	halt();
-	halt();
-	halt();
-	pr_cont("OK\n");
-}
-
 /*
  * Check whether we are able to run this kernel safely on SMP.
  *
@@ -129,7 +103,6 @@ void __init check_bugs(void)
 	print_cpu_info(&boot_cpu_data);
 #endif
 	check_config();
-	check_hlt();
 	init_utsname()->machine[1] =
 		'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 	alternative_instructions();
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 3286a92..e280253 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -28,7 +28,6 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
 {
 	seq_printf(m,
 		   "fdiv_bug\t: %s\n"
-		   "hlt_bug\t\t: %s\n"
 		   "f00f_bug\t: %s\n"
 		   "coma_bug\t: %s\n"
 		   "fpu\t\t: %s\n"
@@ -36,7 +35,6 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
 		   "cpuid level\t: %d\n"
 		   "wp\t\t: %s\n",
 		   c->fdiv_bug ? "yes" : "no",
-		   c->hlt_works_ok ? "no" : "yes",
 		   c->f00f_bug ? "yes" : "no",
 		   c->coma_bug ? "yes" : "no",
 		   c->hard_math ? "yes" : "no",
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index cd5a4c9..aef852e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -415,10 +415,8 @@ void stop_this_cpu(void *dummy)
 	set_cpu_online(smp_processor_id(), false);
 	disable_local_APIC();
 
-	for (;;) {
-		if (hlt_works(smp_processor_id()))
-			halt();
-	}
+	for (;;)
+		halt();
 }
 
 /*
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 2b73b5c..94eac5c 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -556,9 +556,6 @@ void __init xen_arch_setup(void)
 	       COMMAND_LINE_SIZE : MAX_GUEST_CMDLINE);
 
 	/* Set up idle, making sure it calls safe_halt() pvop */
-#ifdef CONFIG_X86_32
-	boot_cpu_data.hlt_works_ok = 1;
-#endif
 	disable_cpuidle();
 	disable_cpufreq();
 	WARN_ON(xen_set_default_idle());
-- 
1.8.1.3.535.ga923c31

Re: [PATCH 2/2 v2] x86 idle: remove 32-bit-only "no-hlt" parameter, hlt_works_ok flag

[Borislav Petkov]

On Sun, Feb 10, 2013 at 04:37:27PM -0500, Len Brown wrote:
> From: Len Brown <len.brown@intel.com>
> 
> Remove 32-bit x86 a cmdline param "no-hlt",
> and the cpuinfo_x86.hlt_works_ok that it sets.
> 
> If a user wants to avoid HLT, then "idle=poll"
> is much more useful, as it avoids invocation of HLT
> in idle, while "no-hlt" failed to do so.
> 
> Indeed, hlt_works_ok was consulted in only 3 places.
> 
> First, in /proc/cpuinfo where "hlt_bug yes"
> would be printed if and only if the user booted
> the system with "no-hlt" -- as there was no other code
> to set that flag.
> 
> Second, check_hlt() would not invoke halt() if "no-hlt"
> were on the cmdline.
> 
> Third, it was consulted in stop_this_cpu(), which is invoked
> by native_machine_halt()/reboot_interrupt()/smp_stop_nmi_callback() --
> all cases where the machine is being shutdown/reset.
> The flag was not consulted in the more frequently invoked
> play_dead()/hlt_play_dead() used in processor offline and suspend.
> 
> Since Linux-3.0 there has been a run-time notice upon "no-hlt" invocations
> indicating that it would be removed in 2012.
> 
> Signed-off-by: Len Brown <len.brown@intel.com>
> Cc: x86@kernel.org
> ---
> v2: remove also check_hlt()

[ … ]

> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index 3286a92..e280253 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -28,7 +28,6 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
>  {
>  	seq_printf(m,
>  		   "fdiv_bug\t: %s\n"
> -		   "hlt_bug\t\t: %s\n"

Are we fine with changing /proc/cpuinfo output? We tend to consider it
an API to userspace, judging by past experience...

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: [PATCH 2/2 v2] x86 idle: remove 32-bit-only "no-hlt" parameter, hlt_works_ok flag

[H. Peter Anvin]

Yes... safer that way.

Borislav Petkov <bp@alien8.de> wrote:

>On Sun, Feb 10, 2013 at 04:37:27PM -0500, Len Brown wrote:
>> From: Len Brown <len.brown@intel.com>
>> 
>> Remove 32-bit x86 a cmdline param "no-hlt",
>> and the cpuinfo_x86.hlt_works_ok that it sets.
>> 
>> If a user wants to avoid HLT, then "idle=poll"
>> is much more useful, as it avoids invocation of HLT
>> in idle, while "no-hlt" failed to do so.
>> 
>> Indeed, hlt_works_ok was consulted in only 3 places.
>> 
>> First, in /proc/cpuinfo where "hlt_bug yes"
>> would be printed if and only if the user booted
>> the system with "no-hlt" -- as there was no other code
>> to set that flag.
>> 
>> Second, check_hlt() would not invoke halt() if "no-hlt"
>> were on the cmdline.
>> 
>> Third, it was consulted in stop_this_cpu(), which is invoked
>> by native_machine_halt()/reboot_interrupt()/smp_stop_nmi_callback()
>--
>> all cases where the machine is being shutdown/reset.
>> The flag was not consulted in the more frequently invoked
>> play_dead()/hlt_play_dead() used in processor offline and suspend.
>> 
>> Since Linux-3.0 there has been a run-time notice upon "no-hlt"
>invocations
>> indicating that it would be removed in 2012.
>> 
>> Signed-off-by: Len Brown <len.brown@intel.com>
>> Cc: x86@kernel.org
>> ---
>> v2: remove also check_hlt()
>
>[ … ]
>
>> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
>> index 3286a92..e280253 100644
>> --- a/arch/x86/kernel/cpu/proc.c
>> +++ b/arch/x86/kernel/cpu/proc.c
>> @@ -28,7 +28,6 @@ static void show_cpuinfo_misc(struct seq_file *m,
>struct cpuinfo_x86 *c)
>>  {
>>  	seq_printf(m,
>>  		   "fdiv_bug\t: %s\n"
>> -		   "hlt_bug\t\t: %s\n"
>
>Are we fine with changing /proc/cpuinfo output? We tend to consider it
>an API to userspace, judging by past experience...

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.