Re: [patch]: fixing of pmtimer overflow that make Cx states timeincorrect

[yakui_zhao]

On Tue, 2009-01-27 at 14:52 +0800, Andrew Morton wrote:
> The fix looks reasonable to me.
> 
> Please always cc linux-acpi@xxxxxxxxxxxxxxx on acpi patches.
> 
> The patch was quite a mess: inlined code plus an attachment, mangled
> email headers, funny characters in the email body, 300-column lines,
> etc.
> 
> I reproduce a cleaned up copy below.
Thanks for the clean up.
But it seems that there exists a potential overflow.
In the clean-up patch the data type of idle_time is defined as u32.
And the idle_time will be converted to sleep_tick by using the macro
definition of US_TO_PM_TIMER. 
>#define US_TO_PM_TIMER_TICKS(t) ((t*(PM_TIMER_FREQUENCY/1000))/1000)
 If the idle_time is more than 4.687s, the overflow will happen. 
 So the interval variable(idle_time) had better be defined as 64-bit
type.  

In fact the following patch is already updated based on the Venki's
suggestion. 
    The monotonic time is not required while getting the C-state sleep
state. In such case the function of ktime_get_real is enough 

thanks.

   
> 
> It's a bit odd that several of these functions (for example,
> acpi_idle_enter_bm()) return number-of-microseconds in a plain `int'. 
> It should be an unsigned scalar - `unsigned int', `u32', `u64', etc.

> 
> Also, all those functions have kerneldoc comments, but none of them
> document the function's return value, which is a rather important part
> of the interface!
> 
> Oh well.
> 
> 
> 
> From: Alex Shi <alex.shi@xxxxxxxxx>
> 
> We found Cx states time abnormal in our some of machines which have 16
> LCPUs, the C0 take too many time while system is really idle when kernel
> enabled tickless and highres.  powertop output is below: 
> 
>      PowerTOP version 1.9       (C) 2007 Intel Corporation
> 
> Cn                Avg residency       P-states (frequencies)
> C0 (cpu running)        (40.5%)         2.53 Ghz     0.0%
> C1                0.0ms ( 0.0%)         2.53 Ghz     0.0%
> C2              128.8ms (59.5%)         2.40 Ghz     0.0%
>                                         1.60 Ghz   100.0%
> 
> 
> Wakeups-from-idle per second :  4.7     interval: 20.0s
> no ACPI power usage estimate available
> 
> Top causes for wakeups:
>   41.4% ( 24.9)       <interrupt> : extra timer interrupt 
>   20.2% ( 12.2)     <kernel core> : usb_hcd_poll_rh_status (rh_timer_func)
> 
> 
> After tacking detailed for this issue, Yakui and I find it is due to 24
> bit PM timer overflows when some of cpu sleep more than 4 seconds.  With
> tickless kernel, the CPU want to sleep as much as possible when system
> idle.  But the Cx sleep time are recorded by pmtimer which length is
> determined by BIOS.  The current Cx time was gotten in the following
> function from driver/acpi/processor_idle.c:
> 
> static inline u32 ticks_elapsed(u32 t1, u32 t2)
> {
>        if (t2 >= t1)
>                return (t2 - t1);
>        else if (!(acpi_gbl_FADT.flags & ACPI_FADT_32BIT_TIMER))
>                return (((0x00FFFFFF - t1) + t2) & 0x00FFFFFF);
>        else
>                return ((0xFFFFFFFF - t1) + t2);
> }
> 
> If pmtimer is 24 bits and it take 5 seconds from t1 to t2, in above
> function, just about 1 seconds ticks was recorded.  So the Cx time will be
> reduced about 4 seconds.  and this is why we see above powertop output.  
> 
> 
> To resolve this problem, Yakui and I use ktime_get() to record the Cx
> states time instead of PM timer as the following patch.  the patch was
> tested with i386/x86_64 modes on several platforms.  and the Cx states
> time become good.  this patch do not fully remove PM timer for Cx idle
> time recording.  Maybe it can be recovered if the PM timer get improved in
> hardware.
> 
> Signed-off-by: Alex Shi <alex.shi@xxxxxxxxx>
> Signed-off-by: Yakui.zhao <yakui.zhao@xxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 
>  drivers/acpi/processor_idle.c |   78 +++++++++++++-------------------
>  1 file changed, 34 insertions(+), 44 deletions(-)
> 
> diff -puN drivers/acpi/processor_idle.c~fixing-of-pmtimer-overflow-that-make-cx-states-time-incorrect drivers/acpi/processor_idle.c
> --- a/drivers/acpi/processor_idle.c~fixing-of-pmtimer-overflow-that-make-cx-states-time-incorrect
> +++ a/drivers/acpi/processor_idle.c
> @@ -185,25 +185,6 @@ static struct dmi_system_id __cpuinitdat
>  	{},
>  };
>  
> -static inline u32 ticks_elapsed(u32 t1, u32 t2)
> -{
> -	if (t2 >= t1)
> -		return (t2 - t1);
> -	else if (!(acpi_gbl_FADT.flags & ACPI_FADT_32BIT_TIMER))
> -		return (((0x00FFFFFF - t1) + t2) & 0x00FFFFFF);
> -	else
> -		return ((0xFFFFFFFF - t1) + t2);
> -}
> -
> -static inline u32 ticks_elapsed_in_us(u32 t1, u32 t2)
> -{
> -	if (t2 >= t1)
> -		return PM_TIMER_TICKS_TO_US(t2 - t1);
> -	else if (!(acpi_gbl_FADT.flags & ACPI_FADT_32BIT_TIMER))
> -		return PM_TIMER_TICKS_TO_US(((0x00FFFFFF - t1) + t2) & 0x00FFFFFF);
> -	else
> -		return PM_TIMER_TICKS_TO_US((0xFFFFFFFF - t1) + t2);
> -}
>  
>  /*
>   * Callers should disable interrupts before the call and enable
> @@ -397,7 +378,8 @@ static void acpi_processor_idle(void)
>  	struct acpi_processor_cx *cx = NULL;
>  	struct acpi_processor_cx *next_state = NULL;
>  	int sleep_ticks = 0;
> -	u32 t1, t2 = 0;
> +	ktime_t  kt1, kt2;
> +	u32 idle_time;
>  
>  	/*
>  	 * Interrupts must be disabled during bus mastering calculations and
> @@ -543,15 +525,16 @@ static void acpi_processor_idle(void)
>  		break;
>  
>  	case ACPI_STATE_C2:
> -		/* Get start time (ticks) */
> -		t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +		/* Get start time  */
> +		kt1 = ktime_get();
>  		/* Tell the scheduler that we are going deep-idle: */
>  		sched_clock_idle_sleep_event();
>  		/* Invoke C2 */
>  		acpi_state_timer_broadcast(pr, cx, 1);
>  		acpi_cstate_enter(cx);
> -		/* Get end time (ticks) */
> -		t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +		/* Get end time */
> +		kt2 = ktime_get();
> +		idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
>  
>  #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
>  		/* TSC halts in C2, so notify users */
> @@ -559,7 +542,7 @@ static void acpi_processor_idle(void)
>  			mark_tsc_unstable("possible TSC halt in C2");
>  #endif
>  		/* Compute time (ticks) that we were actually asleep */
> -		sleep_ticks = ticks_elapsed(t1, t2);
> +		sleep_ticks = US_TO_PM_TIMER_TICKS( idle_time);
>  
>  		/* Tell the scheduler how much we idled: */
>  		sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
> @@ -604,14 +587,15 @@ static void acpi_processor_idle(void)
>  			ACPI_FLUSH_CPU_CACHE();
>  		}
>  
> -		/* Get start time (ticks) */
> -		t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +		/* Get start time  */
> +		kt1 = ktime_get();
>  		/* Invoke C3 */
>  		/* Tell the scheduler that we are going deep-idle: */
>  		sched_clock_idle_sleep_event();
>  		acpi_cstate_enter(cx);
> -		/* Get end time (ticks) */
> -		t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +		/* Get end time  */
> +		kt2 = ktime_get();
> +		idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
>  		if (pr->flags.bm_check && pr->flags.bm_control) {
>  			/* Enable bus master arbitration */
>  			atomic_dec(&c3_cpu_count);
> @@ -624,7 +608,7 @@ static void acpi_processor_idle(void)
>  			mark_tsc_unstable("TSC halts in C3");
>  #endif
>  		/* Compute time (ticks) that we were actually asleep */
> -		sleep_ticks = ticks_elapsed(t1, t2);
> +		sleep_ticks = US_TO_PM_TIMER_TICKS( idle_time);
>  		/* Tell the scheduler how much we idled: */
>  		sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
>  
> @@ -1455,7 +1439,8 @@ static inline void acpi_idle_do_entry(st
>  static int acpi_idle_enter_c1(struct cpuidle_device *dev,
>  			      struct cpuidle_state *state)
>  {
> -	u32 t1, t2;
> +	ktime_t  kt1, kt2;
> +	u32 idle_time;
>  	struct acpi_processor *pr;
>  	struct acpi_processor_cx *cx = cpuidle_get_statedata(state);
>  
> @@ -1476,14 +1461,15 @@ static int acpi_idle_enter_c1(struct cpu
>  	if (pr->flags.bm_check)
>  		acpi_idle_update_bm_rld(pr, cx);
>  
> -	t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +	kt1 = ktime_get();
>  	acpi_idle_do_entry(cx);
> -	t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +	kt2 = ktime_get();
> +	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
>  
>  	local_irq_enable();
>  	cx->usage++;
>  
> -	return ticks_elapsed_in_us(t1, t2);
> +	return idle_time;
>  }
>  
>  /**
> @@ -1496,7 +1482,8 @@ static int acpi_idle_enter_simple(struct
>  {
>  	struct acpi_processor *pr;
>  	struct acpi_processor_cx *cx = cpuidle_get_statedata(state);
> -	u32 t1, t2;
> +	ktime_t  kt1, kt2;
> +	u32 idle_time;
>  	int sleep_ticks = 0;
>  
>  	pr = __get_cpu_var(processors);
> @@ -1533,18 +1520,19 @@ static int acpi_idle_enter_simple(struct
>  	if (cx->type == ACPI_STATE_C3)
>  		ACPI_FLUSH_CPU_CACHE();
>  
> -	t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +	kt1 = ktime_get();
>  	/* Tell the scheduler that we are going deep-idle: */
>  	sched_clock_idle_sleep_event();
>  	acpi_idle_do_entry(cx);
> -	t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +	kt2 = ktime_get();
> +	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
>  
>  #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
>  	/* TSC could halt in idle, so notify users */
>  	if (tsc_halts_in_c(cx->type))
>  		mark_tsc_unstable("TSC halts in idle");;
>  #endif
> -	sleep_ticks = ticks_elapsed(t1, t2);
> +	sleep_ticks = US_TO_PM_TIMER_TICKS( idle_time);
>  
>  	/* Tell the scheduler how much we idled: */
>  	sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
> @@ -1556,7 +1544,7 @@ static int acpi_idle_enter_simple(struct
>  
>  	acpi_state_timer_broadcast(pr, cx, 0);
>  	cx->time += sleep_ticks;
> -	return ticks_elapsed_in_us(t1, t2);
> +	return idle_time;
>  }
>  
>  static int c3_cpu_count;
> @@ -1574,7 +1562,8 @@ static int acpi_idle_enter_bm(struct cpu
>  {
>  	struct acpi_processor *pr;
>  	struct acpi_processor_cx *cx = cpuidle_get_statedata(state);
> -	u32 t1, t2;
> +	ktime_t  kt1, kt2;
> +	u32 idle_time;
>  	int sleep_ticks = 0;
>  
>  	pr = __get_cpu_var(processors);
> @@ -1644,9 +1633,10 @@ static int acpi_idle_enter_bm(struct cpu
>  		ACPI_FLUSH_CPU_CACHE();
>  	}
>  
> -	t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +	kt1 = ktime_get();
>  	acpi_idle_do_entry(cx);
> -	t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
> +	kt2 = ktime_get();
> +	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
>  
>  	/* Re-enable bus master arbitration */
>  	if (pr->flags.bm_check && pr->flags.bm_control) {
> @@ -1661,7 +1651,7 @@ static int acpi_idle_enter_bm(struct cpu
>  	if (tsc_halts_in_c(ACPI_STATE_C3))
>  		mark_tsc_unstable("TSC halts in idle");
>  #endif
> -	sleep_ticks = ticks_elapsed(t1, t2);
> +	sleep_ticks = US_TO_PM_TIMER_TICKS(idle_time);
>  	/* Tell the scheduler how much we idled: */
>  	sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
>  
> @@ -1672,7 +1662,7 @@ static int acpi_idle_enter_bm(struct cpu
>  
>  	acpi_state_timer_broadcast(pr, cx, 0);
>  	cx->time += sleep_ticks;
> -	return ticks_elapsed_in_us(t1, t2);
> +	return idle_time;
>  }
>  
>  struct cpuidle_driver acpi_idle_driver = {
> _
> 

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