linux-kernel - Re: Tracing of power:power

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Date:	Fri, 11 Jun 2010 12:26:47 +0200
From:	Ronny Tschüter <Ronny.Tschueter@...dresden.de>
To:	Robert Schöne <robert.schoene@...dresden.de>
CC:	Arjan van de Ven <arjan@...ux.intel.com>, rostedt@...dmis.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Tracing of power:power_start events doesn't work

On 12/05/2010 10:57, Robert Schöne wrote:
> On Wed, den 05.05.2010-05-05, 07:33 -0700 schrieb Arjan van de Ven:
>    
>> On 5/5/2010 7:31, Steven Rostedt wrote:
>>      
>>> On Wed, 2010-05-05 at 16:11 +0200, Ronny Tsch�ter wrote:
>>>
>>>        
>>>>     /*
>>>>      * Include the apic definitions for x86 to have the APIC timer related
>>>> defines
>>>> @@ -796,6 +797,18 @@ static int acpi_idle_bm_check(void)
>>>>      */
>>>>     static inline void acpi_idle_do_entry(struct acpi_processor_cx *cx)
>>>>     {
>>>> +    switch (cx->type) {
>>>> +    case ACPI_STATE_C1:
>>>> +        trace_power_start(POWER_CSTATE, 1);
>>>> +        break;
>>>> +    case ACPI_STATE_C2:
>>>> +        trace_power_start(POWER_CSTATE, 2);
>>>> +        break;
>>>> +    case ACPI_STATE_C3:
>>>> +        trace_power_start(POWER_CSTATE, 3);
>>>> +        break;
>>>> +    }
>>>> +
>>>>          
>>> Depending on gcc, the above can bloat the code since each call to
>>> trace_power_start() is a macro expanded. Try to call it just once.
>>> Perhaps one of the following:
>>>        
>> the code is also incorrect fundamentally.
>> You need to pass in the mwait value or equivalent; the ACPI STATE type is
>> pretty much useless random garbage and should completely be ignored.
>>      
> You're correct for your case (switching to c-state via monitor/mwait).
> But the current implementation is broken too. It works only if your
> kernel uses processor_idle AND monitor/mwait. For all other cases it
> fails - may it be on Ronnys system, that uses IO port based C-states or
> my system, that uses cpu_idle (not processor_idle).
>
> I'd suggest, that it should work for IO port based switches and could be
> included in the syntactic block of that case.
> Afaik, halt means that the processor goes to C1. So in this block, there
> could be a power_start event too with 1 as new state. (Maybe there are
> problems with AMDs C1E which would be reported as C1.)
>
> Robert
>    
Unfortunately the bug still exists in kernel 2.6.34. On my system I'm 
not able to trace power:power_start events, because they are not 
reported. Regarding to the preceding comments I moved my code snippet 
into the IO port based C-state part of acpi_idle_do_entry(). Therefore 
it should not interfere with the other two C-state calls in this function.
Furthermore a lot of other code sequences in processor_idle.c use the 
ACPI STATE type in if- or switch-statements. So I don't think that ACPI 
STATE type is useless garbage.

Finally here is my new patch:


diff --git a/old/processor_idle.c b/new/processor_idle.c
index 5939e7f..5818522 100644
--- a/old/processor_idle.c
+++ b/new/processor_idle.c
@@ -43,6 +43,7 @@
  #include <linux/clockchips.h>
  #include <linux/cpuidle.h>
  #include <linux/irqflags.h>
+#include <trace/events/power.h>

  /*
   * Include the apic definitions for x86 to have the APIC timer related 
defines
@@ -807,6 +808,10 @@ static inline void acpi_idle_do_entry(struct 
acpi_processor_cx *cx)
      } else {
          int unused;
          /* IO port based C-state */
+        trace_power_start(POWER_CSTATE,
+        cx->type == ACPI_STATE_C1 ? 1 :
+        cx->type == ACPI_STATE_C2 ? 2 :
+        3);
          inb(cx->address);
          /* Dummy wait op - must do something useless after P_LVL2 read
             because chipsets cannot guarantee that STPCLK# signal
--
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