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

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Date:	Tue, 19 Nov 2013 13:06:30 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org,
	rjw@...ysocki.net, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, shaohua.li@...el.com,
	rui.zhang@...el.com, Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>, hpa@...or.com
Subject: Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

On Tue, 19 Nov 2013 16:13:38 +0100
Peter Zijlstra <peterz@...radead.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@...ux.intel.com
> Cc: arjan@...ux.intel.com
> Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Peter Zijlstra <peterz@...radead.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]
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