acpi_pad mwait usage

acpi_pad mwait usage

[Peter Zijlstra]

Hi Len, Rafeal,

I stumbled over acpi_pad (yuck! ;-), but noticed that you don't set the
task in polling mode while using mwait. This means we'll still happily
send an IPI to wake you up.

A little something like the below should do; you might even be able to
remove the smp_mb() but since it is completely undocumented (another
fail) I couldn't tell if the implied barrier in
current_set_polling_and_test() suffices to replace it, so I left it.

If it compiles and works; change it to a proper SOB:

Maybe-Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
 drivers/acpi/acpi_pad.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c
index fc6008fbce35..e9126efe7786 100644
--- a/drivers/acpi/acpi_pad.c
+++ b/drivers/acpi/acpi_pad.c
@@ -195,8 +195,10 @@ static int power_saving_thread(void *data)
 
 			__monitor((void *)&current_thread_info()->flags, 0, 0);
 			smp_mb();
-			if (!need_resched())
+			if (!current_set_polling_and_test()) {
 				__mwait(power_saving_mwait_eax, 1);
+				__current_clr_polling();
+			}
 
 			start_critical_timings();
 			if (lapic_marked_unstable)

Re: acpi_pad mwait usage

[Peter Zijlstra]

On Tue, Nov 19, 2013 at 10:00:19AM +0100, Peter Zijlstra wrote:
> Hi Len, Rafeal,
> 
> I stumbled over acpi_pad (yuck! ;-), but noticed that you don't set the
> task in polling mode while using mwait. This means we'll still happily
> send an IPI to wake you up.
> 
> A little something like the below should do; you might even be able to
> remove the smp_mb() but since it is completely undocumented (another
> fail) I couldn't tell if the implied barrier in
> current_set_polling_and_test() suffices to replace it, so I left it.
> 
> If it compiles and works; change it to a proper SOB:
> 
> Maybe-Signed-off-by: Peter Zijlstra <peterz@infradead.org>

Of course one such driver is insufficient and you lot needed a second;
same issue:

---
 drivers/thermal/intel_powerclamp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
index 8f181b3f842b..d8111e1ac62e 100644
--- a/drivers/thermal/intel_powerclamp.c
+++ b/drivers/thermal/intel_powerclamp.c
@@ -439,8 +439,11 @@ static int clamp_thread(void *arg)
 			local_touch_nmi();
 			stop_critical_timings();
 			__monitor((void *)&current_thread_info()->flags, 0, 0);
-			cpu_relax(); /* allow HT sibling to run */
-			__mwait(eax, ecx);
+			if (!current_set_polling_and_test()) {
+				cpu_relax(); /* allow HT sibling to run */
+				__mwait(eax, ecx);
+				__current_clr_polling();
+			}
 			start_critical_timings();
 			atomic_inc(&idle_wakeup_counter);
 		}

[PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Peter Zijlstra]

People seem to delight in writing wrong and broken mwait idle routines;
collapse the lot.

This leaves mwait_play_dead() the sole remaining user of __mwait() and
new __mwait() users are probably doing it wrong.

Also remove __sti_mwait() as its unused.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---

Mike, does this cure your core2?

 arch/x86/include/asm/mwait.h       | 42 ++++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/processor.h   | 23 ---------------------
 arch/x86/kernel/acpi/cstate.c      | 23 ---------------------
 drivers/acpi/acpi_pad.c            |  5 +----
 drivers/acpi/processor_idle.c      | 15 --------------
 drivers/idle/intel_idle.c          |  8 +-------
 drivers/thermal/intel_powerclamp.c |  4 +---
 7 files changed, 45 insertions(+), 75 deletions(-)

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 2f366d0ac6b4..80014dade987 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -1,6 +1,8 @@
 #ifndef _ASM_X86_MWAIT_H
 #define _ASM_X86_MWAIT_H
 
+#include <linux/sched.h>
+
 #define MWAIT_SUBSTATE_MASK		0xf
 #define MWAIT_CSTATE_MASK		0xf
 #define MWAIT_SUBSTATE_SIZE		4
@@ -13,4 +15,44 @@
 
 #define MWAIT_ECX_INTERRUPT_BREAK	0x1
 
+static inline void __monitor(const void *eax, unsigned long ecx,
+			     unsigned long edx)
+{
+	/* "monitor %eax, %ecx, %edx;" */
+	asm volatile(".byte 0x0f, 0x01, 0xc8;"
+		     :: "a" (eax), "c" (ecx), "d"(edx));
+}
+
+static inline void __mwait(unsigned long eax, unsigned long ecx)
+{
+	/* "mwait %eax, %ecx;" */
+	asm volatile(".byte 0x0f, 0x01, 0xc9;"
+		     :: "a" (eax), "c" (ecx));
+}
+
+/*
+ * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
+ * which can obviate IPI to trigger checking of need_resched.
+ * We execute MONITOR against need_resched and enter optimized wait state
+ * through MWAIT. Whenever someone changes need_resched, we would be woken
+ * up from MWAIT (without an IPI).
+ *
+ * New with Core Duo processors, MWAIT can take some hints based on CPU
+ * capability.
+ */
+static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
+{
+	if (need_resched())
+		return;
+
+	if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
+		clflush((void *)&current_thread_info()->flags);
+
+	__monitor((void *)&current_thread_info()->flags, 0, 0);
+	if (!current_set_polling_and_test())
+		__mwait(eax, ecx);
+
+	__current_clr_polling();
+}
+
 #endif /* _ASM_X86_MWAIT_H */
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 7b034a4057f9..24821f5768bc 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -700,29 +700,6 @@ static inline void sync_core(void)
 #endif
 }
 
-static inline void __monitor(const void *eax, unsigned long ecx,
-			     unsigned long edx)
-{
-	/* "monitor %eax, %ecx, %edx;" */
-	asm volatile(".byte 0x0f, 0x01, 0xc8;"
-		     :: "a" (eax), "c" (ecx), "d"(edx));
-}
-
-static inline void __mwait(unsigned long eax, unsigned long ecx)
-{
-	/* "mwait %eax, %ecx;" */
-	asm volatile(".byte 0x0f, 0x01, 0xc9;"
-		     :: "a" (eax), "c" (ecx));
-}
-
-static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
-{
-	trace_hardirqs_on();
-	/* "mwait %eax, %ecx;" */
-	asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
-		     :: "a" (eax), "c" (ecx));
-}
-
 extern void select_idle_routine(const struct cpuinfo_x86 *c);
 extern void init_amd_e400_c1e_mask(void);
 
diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index d2b7f27781bc..e69182fd01cf 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -150,29 +150,6 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
 }
 EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
 
-/*
- * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
- * which can obviate IPI to trigger checking of need_resched.
- * We execute MONITOR against need_resched and enter optimized wait state
- * through MWAIT. Whenever someone changes need_resched, we would be woken
- * up from MWAIT (without an IPI).
- *
- * New with Core Duo processors, MWAIT can take some hints based on CPU
- * capability.
- */
-void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
-{
-	if (!need_resched()) {
-		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())
-			__mwait(ax, cx);
-	}
-}
-
 void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cx)
 {
 	unsigned int cpu = smp_processor_id();
diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c
index fc6008fbce35..509452a62f96 100644
--- a/drivers/acpi/acpi_pad.c
+++ b/drivers/acpi/acpi_pad.c
@@ -193,10 +193,7 @@ static int power_saving_thread(void *data)
 					CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
 			stop_critical_timings();
 
-			__monitor((void *)&current_thread_info()->flags, 0, 0);
-			smp_mb();
-			if (!need_resched())
-				__mwait(power_saving_mwait_eax, 1);
+			mwait_idle_with_hints(power_saving_mwait_eax, 1);
 
 			start_critical_timings();
 			if (lapic_marked_unstable)
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 644516d9bde6..f90c56c8379e 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -727,11 +727,6 @@ static int acpi_idle_enter_c1(struct cpuidle_device *dev,
 	if (unlikely(!pr))
 		return -EINVAL;
 
-	if (cx->entry_method == ACPI_CSTATE_FFH) {
-		if (current_set_polling_and_test())
-			return -EINVAL;
-	}
-
 	lapic_timer_state_broadcast(pr, cx, 1);
 	acpi_idle_do_entry(cx);
 
@@ -785,11 +780,6 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
 	if (unlikely(!pr))
 		return -EINVAL;
 
-	if (cx->entry_method == ACPI_CSTATE_FFH) {
-		if (current_set_polling_and_test())
-			return -EINVAL;
-	}
-
 	/*
 	 * Must be done before busmaster disable as we might need to
 	 * access HPET !
@@ -841,11 +831,6 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
 		}
 	}
 
-	if (cx->entry_method == ACPI_CSTATE_FFH) {
-		if (current_set_polling_and_test())
-			return -EINVAL;
-	}
-
 	acpi_unlazy_tlb(smp_processor_id());
 
 	/* Tell the scheduler that we are going deep-idle: */
diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 3226ce98fb18..3b56d76a5bca 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -359,13 +359,7 @@ static int intel_idle(struct cpuidle_device *dev,
 	if (!(lapic_timer_reliable_states & (1 << (cstate))))
 		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
 
-	if (!current_set_polling_and_test()) {
-
-		__monitor((void *)&current_thread_info()->flags, 0, 0);
-		smp_mb();
-		if (!need_resched())
-			__mwait(eax, ecx);
-	}
+	mwait_idle_with_hints(eax, ecx);
 
 	if (!(lapic_timer_reliable_states & (1 << (cstate))))
 		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
index 8f181b3f842b..e8275f2df9af 100644
--- a/drivers/thermal/intel_powerclamp.c
+++ b/drivers/thermal/intel_powerclamp.c
@@ -438,9 +438,7 @@ static int clamp_thread(void *arg)
 			 */
 			local_touch_nmi();
 			stop_critical_timings();
-			__monitor((void *)&current_thread_info()->flags, 0, 0);
-			cpu_relax(); /* allow HT sibling to run */
-			__mwait(eax, ecx);
+			mwait_idle_with_hints(eax, ecx);
 			start_critical_timings();
 			atomic_inc(&idle_wakeup_counter);
 		}

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Rafael J. Wysocki]

On Tuesday, November 19, 2013 12:31:53 PM Peter Zijlstra wrote:
> People seem to delight in writing wrong and broken mwait idle routines;
> collapse the lot.
> 
> This leaves mwait_play_dead() the sole remaining user of __mwait() and
> new __mwait() users are probably doing it wrong.
> 
> Also remove __sti_mwait() as its unused.
> 
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>

For the ACPI part:

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
> 
> Mike, does this cure your core2?
> 
>  arch/x86/include/asm/mwait.h       | 42 ++++++++++++++++++++++++++++++++++++++
>  arch/x86/include/asm/processor.h   | 23 ---------------------
>  arch/x86/kernel/acpi/cstate.c      | 23 ---------------------
>  drivers/acpi/acpi_pad.c            |  5 +----
>  drivers/acpi/processor_idle.c      | 15 --------------
>  drivers/idle/intel_idle.c          |  8 +-------
>  drivers/thermal/intel_powerclamp.c |  4 +---
>  7 files changed, 45 insertions(+), 75 deletions(-)
> 
> diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
> index 2f366d0ac6b4..80014dade987 100644
> --- a/arch/x86/include/asm/mwait.h
> +++ b/arch/x86/include/asm/mwait.h
> @@ -1,6 +1,8 @@
>  #ifndef _ASM_X86_MWAIT_H
>  #define _ASM_X86_MWAIT_H
>  
> +#include <linux/sched.h>
> +
>  #define MWAIT_SUBSTATE_MASK		0xf
>  #define MWAIT_CSTATE_MASK		0xf
>  #define MWAIT_SUBSTATE_SIZE		4
> @@ -13,4 +15,44 @@
>  
>  #define MWAIT_ECX_INTERRUPT_BREAK	0x1
>  
> +static inline void __monitor(const void *eax, unsigned long ecx,
> +			     unsigned long edx)
> +{
> +	/* "monitor %eax, %ecx, %edx;" */
> +	asm volatile(".byte 0x0f, 0x01, 0xc8;"
> +		     :: "a" (eax), "c" (ecx), "d"(edx));
> +}
> +
> +static inline void __mwait(unsigned long eax, unsigned long ecx)
> +{
> +	/* "mwait %eax, %ecx;" */
> +	asm volatile(".byte 0x0f, 0x01, 0xc9;"
> +		     :: "a" (eax), "c" (ecx));
> +}
> +
> +/*
> + * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
> + * which can obviate IPI to trigger checking of need_resched.
> + * We execute MONITOR against need_resched and enter optimized wait state
> + * through MWAIT. Whenever someone changes need_resched, we would be woken
> + * up from MWAIT (without an IPI).
> + *
> + * New with Core Duo processors, MWAIT can take some hints based on CPU
> + * capability.
> + */
> +static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
> +{
> +	if (need_resched())
> +		return;
> +
> +	if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
> +		clflush((void *)&current_thread_info()->flags);
> +
> +	__monitor((void *)&current_thread_info()->flags, 0, 0);
> +	if (!current_set_polling_and_test())
> +		__mwait(eax, ecx);
> +
> +	__current_clr_polling();
> +}
> +
>  #endif /* _ASM_X86_MWAIT_H */
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 7b034a4057f9..24821f5768bc 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -700,29 +700,6 @@ static inline void sync_core(void)
>  #endif
>  }
>  
> -static inline void __monitor(const void *eax, unsigned long ecx,
> -			     unsigned long edx)
> -{
> -	/* "monitor %eax, %ecx, %edx;" */
> -	asm volatile(".byte 0x0f, 0x01, 0xc8;"
> -		     :: "a" (eax), "c" (ecx), "d"(edx));
> -}
> -
> -static inline void __mwait(unsigned long eax, unsigned long ecx)
> -{
> -	/* "mwait %eax, %ecx;" */
> -	asm volatile(".byte 0x0f, 0x01, 0xc9;"
> -		     :: "a" (eax), "c" (ecx));
> -}
> -
> -static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
> -{
> -	trace_hardirqs_on();
> -	/* "mwait %eax, %ecx;" */
> -	asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
> -		     :: "a" (eax), "c" (ecx));
> -}
> -
>  extern void select_idle_routine(const struct cpuinfo_x86 *c);
>  extern void init_amd_e400_c1e_mask(void);
>  
> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> index d2b7f27781bc..e69182fd01cf 100644
> --- a/arch/x86/kernel/acpi/cstate.c
> +++ b/arch/x86/kernel/acpi/cstate.c
> @@ -150,29 +150,6 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
>  }
>  EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
>  
> -/*
> - * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
> - * which can obviate IPI to trigger checking of need_resched.
> - * We execute MONITOR against need_resched and enter optimized wait state
> - * through MWAIT. Whenever someone changes need_resched, we would be woken
> - * up from MWAIT (without an IPI).
> - *
> - * New with Core Duo processors, MWAIT can take some hints based on CPU
> - * capability.
> - */
> -void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
> -{
> -	if (!need_resched()) {
> -		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())
> -			__mwait(ax, cx);
> -	}
> -}
> -
>  void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cx)
>  {
>  	unsigned int cpu = smp_processor_id();
> diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c
> index fc6008fbce35..509452a62f96 100644
> --- a/drivers/acpi/acpi_pad.c
> +++ b/drivers/acpi/acpi_pad.c
> @@ -193,10 +193,7 @@ static int power_saving_thread(void *data)
>  					CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
>  			stop_critical_timings();
>  
> -			__monitor((void *)&current_thread_info()->flags, 0, 0);
> -			smp_mb();
> -			if (!need_resched())
> -				__mwait(power_saving_mwait_eax, 1);
> +			mwait_idle_with_hints(power_saving_mwait_eax, 1);
>  
>  			start_critical_timings();
>  			if (lapic_marked_unstable)
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 644516d9bde6..f90c56c8379e 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -727,11 +727,6 @@ static int acpi_idle_enter_c1(struct cpuidle_device *dev,
>  	if (unlikely(!pr))
>  		return -EINVAL;
>  
> -	if (cx->entry_method == ACPI_CSTATE_FFH) {
> -		if (current_set_polling_and_test())
> -			return -EINVAL;
> -	}
> -
>  	lapic_timer_state_broadcast(pr, cx, 1);
>  	acpi_idle_do_entry(cx);
>  
> @@ -785,11 +780,6 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
>  	if (unlikely(!pr))
>  		return -EINVAL;
>  
> -	if (cx->entry_method == ACPI_CSTATE_FFH) {
> -		if (current_set_polling_and_test())
> -			return -EINVAL;
> -	}
> -
>  	/*
>  	 * Must be done before busmaster disable as we might need to
>  	 * access HPET !
> @@ -841,11 +831,6 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  		}
>  	}
>  
> -	if (cx->entry_method == ACPI_CSTATE_FFH) {
> -		if (current_set_polling_and_test())
> -			return -EINVAL;
> -	}
> -
>  	acpi_unlazy_tlb(smp_processor_id());
>  
>  	/* Tell the scheduler that we are going deep-idle: */
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index 3226ce98fb18..3b56d76a5bca 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -359,13 +359,7 @@ static int intel_idle(struct cpuidle_device *dev,
>  	if (!(lapic_timer_reliable_states & (1 << (cstate))))
>  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
>  
> -	if (!current_set_polling_and_test()) {
> -
> -		__monitor((void *)&current_thread_info()->flags, 0, 0);
> -		smp_mb();
> -		if (!need_resched())
> -			__mwait(eax, ecx);
> -	}
> +	mwait_idle_with_hints(eax, ecx);
>  
>  	if (!(lapic_timer_reliable_states & (1 << (cstate))))
>  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
> diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
> index 8f181b3f842b..e8275f2df9af 100644
> --- a/drivers/thermal/intel_powerclamp.c
> +++ b/drivers/thermal/intel_powerclamp.c
> @@ -438,9 +438,7 @@ static int clamp_thread(void *arg)
>  			 */
>  			local_touch_nmi();
>  			stop_critical_timings();
> -			__monitor((void *)&current_thread_info()->flags, 0, 0);
> -			cpu_relax(); /* allow HT sibling to run */
> -			__mwait(eax, ecx);
> +			mwait_idle_with_hints(eax, ecx);
>  			start_critical_timings();
>  			atomic_inc(&idle_wakeup_counter);
>  		}
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Mike Galbraith]

On Tue, 2013-11-19 at 12:31 +0100, Peter Zijlstra wrote: 
> People seem to delight in writing wrong and broken mwait idle routines;
> collapse the lot.
> 
> This leaves mwait_play_dead() the sole remaining user of __mwait() and
> new __mwait() users are probably doing it wrong.
> 
> Also remove __sti_mwait() as its unused.
> 
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> ---
> 
> Mike, does this cure your core2?

Nope.  Maybe an acpi/bios thingy on this box since diags that fired on
lappy during boot did not fire on desktop, and both are core2 booting
same kernel.  I kinda suspect I'll either be stuck with default_idle or
have to resurrect mwait_idle and carry it locally if I want the thing to
work well.  Guess I'll find out if/when I have time to squabble with it.

Meanwhile, desktop box works fine modulo benchmarks, lappy works fine
too, modulo max_cstate=1 scaring mwait_idle_with_hints away, which I
don't care about much.  Neither box is wonderful at rt testing where I
usually boot max_cstate=1, both just became a bit _less_ wonderful :)

-Mike

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Arjan van de Ven]

> diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
> index 8f181b3f842b..e8275f2df9af 100644
> --- a/drivers/thermal/intel_powerclamp.c
> +++ b/drivers/thermal/intel_powerclamp.c
> @@ -438,9 +438,7 @@ static int clamp_thread(void *arg)
>   			 */
>   			local_touch_nmi();
>   			stop_critical_timings();
> -			__monitor((void *)&current_thread_info()->flags, 0, 0);
> -			cpu_relax(); /* allow HT sibling to run */
> -			__mwait(eax, ecx);
> +			mwait_idle_with_hints(eax, ecx);
>   			start_critical_timings();
>   			atomic_inc(&idle_wakeup_counter);
>   		}
>

hmm I take it that mwait_idle_with_hints is the one that also checks need_resched() ?
if so... powerclamp may not want to use that (the whole point is to NOT give the cpu
to tasks!)

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Peter Zijlstra]

On Tue, Nov 19, 2013 at 06:22:43AM -0800, Arjan van de Ven wrote:
> >diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
> >index 8f181b3f842b..e8275f2df9af 100644
> >--- a/drivers/thermal/intel_powerclamp.c
> >+++ b/drivers/thermal/intel_powerclamp.c
> >@@ -438,9 +438,7 @@ static int clamp_thread(void *arg)
> >  			 */
> >  			local_touch_nmi();
> >  			stop_critical_timings();
> >-			__monitor((void *)&current_thread_info()->flags, 0, 0);
> >-			cpu_relax(); /* allow HT sibling to run */
> >-			__mwait(eax, ecx);
> >+			mwait_idle_with_hints(eax, ecx);
> >  			start_critical_timings();
> >  			atomic_inc(&idle_wakeup_counter);
> >  		}
> >
> 
> hmm I take it that mwait_idle_with_hints is the one that also checks need_resched() ?
> if so... powerclamp may not want to use that (the whole point is to NOT give the cpu
> to tasks!)

Of course, you're very much not getting something that wins from
stop_machine or a fifo-99 task.

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Peter Zijlstra]

On Tue, Nov 19, 2013 at 06:22:43AM -0800, Arjan van de Ven wrote:
> >diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
> >index 8f181b3f842b..e8275f2df9af 100644
> >--- a/drivers/thermal/intel_powerclamp.c
> >+++ b/drivers/thermal/intel_powerclamp.c
> >@@ -438,9 +438,7 @@ static int clamp_thread(void *arg)
> >  			 */
> >  			local_touch_nmi();
> >  			stop_critical_timings();
> >-			__monitor((void *)&current_thread_info()->flags, 0, 0);
> >-			cpu_relax(); /* allow HT sibling to run */
> >-			__mwait(eax, ecx);
> >+			mwait_idle_with_hints(eax, ecx);
> >  			start_critical_timings();
> >  			atomic_inc(&idle_wakeup_counter);
> >  		}
> >
> 
> hmm I take it that mwait_idle_with_hints is the one that also checks need_resched() ?
> if so... powerclamp may not want to use that (the whole point is to NOT give the cpu
> to tasks!)

That said, that drive is completely wrecked. It uses
preempt_enable_no_resched() wrong too, it has uncommented barriers..

Dude, wtf are you guys smoking?

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Peter Zijlstra]

On Tue, Nov 19, 2013 at 03:51:43PM +0100, Peter Zijlstra wrote:
> That said, that drive is completely wrecked. It uses
> preempt_enable_no_resched() wrong too, it has uncommented barriers..
> 
> Dude, wtf are you guys smoking?

---
Subject: sched: Take away preempt_enable_no_resched() and friends from modules

There is no way in hell modules are going to play preemption tricks like
this.

Cc: eliezer.tamir@linux.intel.com
Cc: arjan@linux.intel.com
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
 drivers/thermal/intel_powerclamp.c |  2 +-
 include/linux/preempt.h            |  8 +++++++-
 include/net/busy_poll.h            | 15 +++------------
 3 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
index 8f181b3f842b..0a12ddc2eb4c 100644
--- a/drivers/thermal/intel_powerclamp.c
+++ b/drivers/thermal/intel_powerclamp.c
@@ -445,7 +445,7 @@ static int clamp_thread(void *arg)
 			atomic_inc(&idle_wakeup_counter);
 		}
 		tick_nohz_idle_exit();
-		preempt_enable_no_resched();
+		preempt_enable();
 	}
 	del_timer_sync(&wakeup_timer);
 	clear_bit(cpunr, cpu_clamping_mask);
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index a3d9dc8c2c00..3ed2b5335ab4 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -64,7 +64,7 @@ do { \
 } while (0)
 
 #else
-#define preempt_enable() preempt_enable_no_resched()
+#define preempt_enable() sched_preempt_enable_no_resched()
 #define preempt_check_resched() do { } while (0)
 #endif
 
@@ -116,6 +116,12 @@ do { \
 
 #endif /* CONFIG_PREEMPT_COUNT */
 
+#ifdef MODULE
+#undef preempt_enable_no_resched
+#undef preempt_enable_no_resched_notrace
+#undef preempt_check_resched
+#endif
+
 #ifdef CONFIG_PREEMPT_NOTIFIERS
 
 struct preempt_notifier;
diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h
index 829627d7b846..756827a86c2d 100644
--- a/include/net/busy_poll.h
+++ b/include/net/busy_poll.h
@@ -42,27 +42,18 @@ static inline bool net_busy_loop_on(void)
 	return sysctl_net_busy_poll;
 }
 
-/* a wrapper to make debug_smp_processor_id() happy
- * we can use sched_clock() because we don't care much about precision
- * we only care that the average is bounded
- */
-#ifdef CONFIG_DEBUG_PREEMPT
 static inline u64 busy_loop_us_clock(void)
 {
 	u64 rc;
 
+	/* XXX with interrupts enabled sched_clock() can return utter garbage */
+
 	preempt_disable_notrace();
 	rc = sched_clock();
-	preempt_enable_no_resched_notrace();
+	preempt_enable_notrace();
 
 	return rc >> 10;
 }
-#else /* CONFIG_DEBUG_PREEMPT */
-static inline u64 busy_loop_us_clock(void)
-{
-	return sched_clock() >> 10;
-}
-#endif /* CONFIG_DEBUG_PREEMPT */
 
 static inline unsigned long sk_busy_loop_end_time(struct sock *sk)
 {

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Jacob Pan]

On Tue, 19 Nov 2013 16:13:38 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Nov 19, 2013 at 03:51:43PM +0100, Peter Zijlstra wrote:
> > That said, that drive is completely wrecked. It uses
> > preempt_enable_no_resched() wrong too, it has uncommented barriers..
> > 
> > Dude, wtf are you guys smoking?
> 
I applied this patch on top of upstream kernel (801a760) and found out
my machine completely failed to enter idle when nothing is running.
turbostate shows 100% C0. ftrace shows kernel coming in and out of idle
frequently.

Both ACPI idle and intel_idle behaves the same way. I have to do the
following change to allow entering C-states again.

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 80014da..b51d1e1 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -49,10 +49,8 @@ static inline void mwait_idle_with_hints(unsigned
long eax, unsigned long ecx) clflush((void
*)&current_thread_info()->flags); 
        __monitor((void *)&current_thread_info()->flags, 0, 0);
-       if (!current_set_polling_and_test())
+        if (!need_resched())
                __mwait(eax, ecx);
-
-       __current_clr_polling();
 }
 
 #endif /* _ASM_X86_MWAIT_H */

Did i miss any other patches?

Jacob

> ---
> Subject: sched: Take away preempt_enable_no_resched() and friends
> from modules
> 
> There is no way in hell modules are going to play preemption tricks
> like this.
> 
> Cc: eliezer.tamir@linux.intel.com
> Cc: arjan@linux.intel.com
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> ---
>  drivers/thermal/intel_powerclamp.c |  2 +-
>  include/linux/preempt.h            |  8 +++++++-
>  include/net/busy_poll.h            | 15 +++------------
>  3 files changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/thermal/intel_powerclamp.c
> b/drivers/thermal/intel_powerclamp.c index 8f181b3f842b..0a12ddc2eb4c
> 100644 --- a/drivers/thermal/intel_powerclamp.c
> +++ b/drivers/thermal/intel_powerclamp.c
> @@ -445,7 +445,7 @@ static int clamp_thread(void *arg)
>  			atomic_inc(&idle_wakeup_counter);
>  		}
>  		tick_nohz_idle_exit();
> -		preempt_enable_no_resched();
> +		preempt_enable();
>  	}
>  	del_timer_sync(&wakeup_timer);
>  	clear_bit(cpunr, cpu_clamping_mask);
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index a3d9dc8c2c00..3ed2b5335ab4 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -64,7 +64,7 @@ do { \
>  } while (0)
>  
>  #else
> -#define preempt_enable() preempt_enable_no_resched()
> +#define preempt_enable() sched_preempt_enable_no_resched()
>  #define preempt_check_resched() do { } while (0)
>  #endif
>  
> @@ -116,6 +116,12 @@ do { \
>  
>  #endif /* CONFIG_PREEMPT_COUNT */
>  
> +#ifdef MODULE
> +#undef preempt_enable_no_resched
> +#undef preempt_enable_no_resched_notrace
> +#undef preempt_check_resched
> +#endif
> +
>  #ifdef CONFIG_PREEMPT_NOTIFIERS
>  
>  struct preempt_notifier;
> diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h
> index 829627d7b846..756827a86c2d 100644
> --- a/include/net/busy_poll.h
> +++ b/include/net/busy_poll.h
> @@ -42,27 +42,18 @@ static inline bool net_busy_loop_on(void)
>  	return sysctl_net_busy_poll;
>  }
>  
> -/* a wrapper to make debug_smp_processor_id() happy
> - * we can use sched_clock() because we don't care much about
> precision
> - * we only care that the average is bounded
> - */
> -#ifdef CONFIG_DEBUG_PREEMPT
>  static inline u64 busy_loop_us_clock(void)
>  {
>  	u64 rc;
>  
> +	/* XXX with interrupts enabled sched_clock() can return
> utter garbage */ +
>  	preempt_disable_notrace();
>  	rc = sched_clock();
> -	preempt_enable_no_resched_notrace();
> +	preempt_enable_notrace();
>  
>  	return rc >> 10;
>  }
> -#else /* CONFIG_DEBUG_PREEMPT */
> -static inline u64 busy_loop_us_clock(void)
> -{
> -	return sched_clock() >> 10;
> -}
> -#endif /* CONFIG_DEBUG_PREEMPT */
>  
>  static inline unsigned long sk_busy_loop_end_time(struct sock *sk)
>  {
> 

[Jacob Pan]

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Peter Zijlstra]

On Tue, Nov 19, 2013 at 01:06:30PM -0800, Jacob Pan wrote:
> On Tue, 19 Nov 2013 16:13:38 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Tue, Nov 19, 2013 at 03:51:43PM +0100, Peter Zijlstra wrote:
> > > That said, that drive is completely wrecked. It uses
> > > preempt_enable_no_resched() wrong too, it has uncommented barriers..
> > > 
> > > Dude, wtf are you guys smoking?
> > 
> I applied this patch on top of upstream kernel (801a760) and found out
> my machine completely failed to enter idle when nothing is running.
> turbostate shows 100% C0. ftrace shows kernel coming in and out of idle
> frequently.
> 
> Both ACPI idle and intel_idle behaves the same way. I have to do the
> following change to allow entering C-states again.
> 
> diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
> index 80014da..b51d1e1 100644
> --- a/arch/x86/include/asm/mwait.h
> +++ b/arch/x86/include/asm/mwait.h
> @@ -49,10 +49,8 @@ static inline void mwait_idle_with_hints(unsigned
> long eax, unsigned long ecx) clflush((void
> *)&current_thread_info()->flags); 
>         __monitor((void *)&current_thread_info()->flags, 0, 0);
> -       if (!current_set_polling_and_test())
> +        if (!need_resched())
>                 __mwait(eax, ecx);
> -
> -       __current_clr_polling();
>  }
>  
>  #endif /* _ASM_X86_MWAIT_H */

That doesn't make any sense; current_set_polling_and_test() returns the
same thing need_resched() does.

But you're right, intel_idle resides 100% in C0 and acpi_idle has 100%
C1 residency... most weird.

/me goes prod at it

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Peter Zijlstra]

On Wed, Nov 20, 2013 at 11:28:03AM +0100, Peter Zijlstra wrote:
> On Tue, Nov 19, 2013 at 01:06:30PM -0800, Jacob Pan wrote:
> > I applied this patch on top of upstream kernel (801a760) and found out
> > my machine completely failed to enter idle when nothing is running.
> > turbostate shows 100% C0. ftrace shows kernel coming in and out of idle
> > frequently.
> > 
> > Both ACPI idle and intel_idle behaves the same way. I have to do the
> > following change to allow entering C-states again.

> That doesn't make any sense; current_set_polling_and_test() returns the
> same thing need_resched() does.
> 
> But you're right, intel_idle resides 100% in C0 and acpi_idle has 100%
> C1 residency... most weird.

So pretty silly actually; you cannot do a store (any store) in between
monitor and mwait.

The below version seems to work properly again with both acpi_idle and
intel_idle.

Now to go make that preempt_disable_no_resched cleanup compile.. :-)

---
Subject: x86, acpi, idle: Restructure the mwait idle routines
From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 19 Nov 2013 12:31:53 +0100

People seem to delight in writing wrong and broken mwait idle routines;
collapse the lot.

This leaves mwait_play_dead() the sole remaining user of __mwait() and
new __mwait() users are probably doing it wrong.

Also remove __sti_mwait() as its unused.

Cc: arjan@linux.intel.com
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hpa@zytor.com
Cc: lenb@kernel.org
Cc: shaohua.li@intel.com
Cc: rui.zhang@intel.com
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
 arch/x86/include/asm/mwait.h       |   40 +++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/processor.h   |   23 ---------------------
 arch/x86/kernel/acpi/cstate.c      |   23 ---------------------
 drivers/acpi/acpi_pad.c            |    5 ----
 drivers/acpi/processor_idle.c      |   15 -------------
 drivers/idle/intel_idle.c          |    8 -------
 drivers/thermal/intel_powerclamp.c |    4 ---
 7 files changed, 43 insertions(+), 75 deletions(-)

--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -1,6 +1,8 @@
 #ifndef _ASM_X86_MWAIT_H
 #define _ASM_X86_MWAIT_H
 
+#include <linux/sched.h>
+
 #define MWAIT_SUBSTATE_MASK		0xf
 #define MWAIT_CSTATE_MASK		0xf
 #define MWAIT_SUBSTATE_SIZE		4
@@ -13,4 +15,42 @@
 
 #define MWAIT_ECX_INTERRUPT_BREAK	0x1
 
+static inline void __monitor(const void *eax, unsigned long ecx,
+			     unsigned long edx)
+{
+	/* "monitor %eax, %ecx, %edx;" */
+	asm volatile(".byte 0x0f, 0x01, 0xc8;"
+		     :: "a" (eax), "c" (ecx), "d"(edx));
+}
+
+static inline void __mwait(unsigned long eax, unsigned long ecx)
+{
+	/* "mwait %eax, %ecx;" */
+	asm volatile(".byte 0x0f, 0x01, 0xc9;"
+		     :: "a" (eax), "c" (ecx));
+}
+
+/*
+ * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
+ * which can obviate IPI to trigger checking of need_resched.
+ * We execute MONITOR against need_resched and enter optimized wait state
+ * through MWAIT. Whenever someone changes need_resched, we would be woken
+ * up from MWAIT (without an IPI).
+ *
+ * New with Core Duo processors, MWAIT can take some hints based on CPU
+ * capability.
+ */
+static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
+{
+	if (!current_set_polling_and_test()) {
+		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
+			clflush((void *)&current_thread_info()->flags);
+
+		__monitor((void *)&current_thread_info()->flags, 0, 0);
+		if (!need_resched())
+			__mwait(eax, ecx);
+	}
+	__current_clr_polling();
+}
+
 #endif /* _ASM_X86_MWAIT_H */
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -700,29 +700,6 @@ static inline void sync_core(void)
 #endif
 }
 
-static inline void __monitor(const void *eax, unsigned long ecx,
-			     unsigned long edx)
-{
-	/* "monitor %eax, %ecx, %edx;" */
-	asm volatile(".byte 0x0f, 0x01, 0xc8;"
-		     :: "a" (eax), "c" (ecx), "d"(edx));
-}
-
-static inline void __mwait(unsigned long eax, unsigned long ecx)
-{
-	/* "mwait %eax, %ecx;" */
-	asm volatile(".byte 0x0f, 0x01, 0xc9;"
-		     :: "a" (eax), "c" (ecx));
-}
-
-static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
-{
-	trace_hardirqs_on();
-	/* "mwait %eax, %ecx;" */
-	asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
-		     :: "a" (eax), "c" (ecx));
-}
-
 extern void select_idle_routine(const struct cpuinfo_x86 *c);
 extern void init_amd_e400_c1e_mask(void);
 
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -150,29 +150,6 @@ int acpi_processor_ffh_cstate_probe(unsi
 }
 EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
 
-/*
- * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
- * which can obviate IPI to trigger checking of need_resched.
- * We execute MONITOR against need_resched and enter optimized wait state
- * through MWAIT. Whenever someone changes need_resched, we would be woken
- * up from MWAIT (without an IPI).
- *
- * New with Core Duo processors, MWAIT can take some hints based on CPU
- * capability.
- */
-void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
-{
-	if (!need_resched()) {
-		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())
-			__mwait(ax, cx);
-	}
-}
-
 void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cx)
 {
 	unsigned int cpu = smp_processor_id();
--- a/drivers/acpi/acpi_pad.c
+++ b/drivers/acpi/acpi_pad.c
@@ -193,10 +193,7 @@ static int power_saving_thread(void *dat
 					CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
 			stop_critical_timings();
 
-			__monitor((void *)&current_thread_info()->flags, 0, 0);
-			smp_mb();
-			if (!need_resched())
-				__mwait(power_saving_mwait_eax, 1);
+			mwait_idle_with_hints(power_saving_mwait_eax, 1);
 
 			start_critical_timings();
 			if (lapic_marked_unstable)
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -727,11 +727,6 @@ static int acpi_idle_enter_c1(struct cpu
 	if (unlikely(!pr))
 		return -EINVAL;
 
-	if (cx->entry_method == ACPI_CSTATE_FFH) {
-		if (current_set_polling_and_test())
-			return -EINVAL;
-	}
-
 	lapic_timer_state_broadcast(pr, cx, 1);
 	acpi_idle_do_entry(cx);
 
@@ -785,11 +780,6 @@ static int acpi_idle_enter_simple(struct
 	if (unlikely(!pr))
 		return -EINVAL;
 
-	if (cx->entry_method == ACPI_CSTATE_FFH) {
-		if (current_set_polling_and_test())
-			return -EINVAL;
-	}
-
 	/*
 	 * Must be done before busmaster disable as we might need to
 	 * access HPET !
@@ -841,11 +831,6 @@ static int acpi_idle_enter_bm(struct cpu
 		}
 	}
 
-	if (cx->entry_method == ACPI_CSTATE_FFH) {
-		if (current_set_polling_and_test())
-			return -EINVAL;
-	}
-
 	acpi_unlazy_tlb(smp_processor_id());
 
 	/* Tell the scheduler that we are going deep-idle: */
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -359,13 +359,7 @@ static int intel_idle(struct cpuidle_dev
 	if (!(lapic_timer_reliable_states & (1 << (cstate))))
 		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
 
-	if (!current_set_polling_and_test()) {
-
-		__monitor((void *)&current_thread_info()->flags, 0, 0);
-		smp_mb();
-		if (!need_resched())
-			__mwait(eax, ecx);
-	}
+	mwait_idle_with_hints(eax, ecx);
 
 	if (!(lapic_timer_reliable_states & (1 << (cstate))))
 		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
--- a/drivers/thermal/intel_powerclamp.c
+++ b/drivers/thermal/intel_powerclamp.c
@@ -438,9 +438,7 @@ static int clamp_thread(void *arg)
 			 */
 			local_touch_nmi();
 			stop_critical_timings();
-			__monitor((void *)&current_thread_info()->flags, 0, 0);
-			cpu_relax(); /* allow HT sibling to run */
-			__mwait(eax, ecx);
+			mwait_idle_with_hints(eax, ecx);
 			start_critical_timings();
 			atomic_inc(&idle_wakeup_counter);
 		}

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Arjan van de Ven]

On 11/20/2013 2:58 AM, Peter Zijlstra wrote:
> On Wed, Nov 20, 2013 at 11:28:03AM +0100, Peter Zijlstra wrote:
>> On Tue, Nov 19, 2013 at 01:06:30PM -0800, Jacob Pan wrote:
>>> I applied this patch on top of upstream kernel (801a760) and found out
>>> my machine completely failed to enter idle when nothing is running.
>>> turbostate shows 100% C0. ftrace shows kernel coming in and out of idle
>>> frequently.
>>>
>>> Both ACPI idle and intel_idle behaves the same way. I have to do the
>>> following change to allow entering C-states again.
>
>> That doesn't make any sense; current_set_polling_and_test() returns the
>> same thing need_resched() does.
>>
>> But you're right, intel_idle resides 100% in C0 and acpi_idle has 100%
>> C1 residency... most weird.
>
> So pretty silly actually; you cannot do a store (any store) in between
> monitor and mwait.

you can
just not to the cacheline you are watching (or things that alias with that)

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Peter Zijlstra]

On Wed, Nov 20, 2013 at 08:24:47AM -0800, Arjan van de Ven wrote:
> On 11/20/2013 2:58 AM, Peter Zijlstra wrote:
> >So pretty silly actually; you cannot do a store (any store) in between
> >monitor and mwait.
> 
> you can
> just not to the cacheline you are watching (or things that alias with that)

Ah indeed, the thread_info::status is in the same cacheline.

Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

[Arjan van de Ven]

On 11/20/2013 8:33 AM, Peter Zijlstra wrote:
> On Wed, Nov 20, 2013 at 08:24:47AM -0800, Arjan van de Ven wrote:
>> On 11/20/2013 2:58 AM, Peter Zijlstra wrote:
>>> So pretty silly actually; you cannot do a store (any store) in between
>>> monitor and mwait.
>>
>> you can
>> just not to the cacheline you are watching (or things that alias with that)
>
> Ah indeed, the thread_info::status is in the same cacheline.
>

you told it to wake on any write to that cacheline
and then you write to it ;-)