Re: [RFC/PATCH] Prevent wasting time to find out get_parent_ip

[Minho Ban]

On 04/25/2012 03:16 AM, Steven Rostedt wrote:
> On Tue, 2012-04-24 at 21:36 +0900, Minho Ban wrote:
>> trace_preempt_on/off looks empty if PREEMPT_TRACER is off. But actually it is
>> spending time to find out get_parent_ip(even CALLER_ADDR for some ARCH) which is
>> in argument. This seems not fair for those who expect to do nothing but increase
>> or decrease count.
>>
> 
> Yuck what an ugly patch. Please don't uglify the C code with #ifdefs!
> 

Yes, I agree.

>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Signed-off-by: Minho Ban <mhban@xxxxxxxxxxx>
>> ---
>>  include/linux/ftrace.h |    3 ---
>>  kernel/sched/core.c    |    5 ++++-
>>  kernel/softirq.c       |    3 ++-
>>  3 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
>> index 72a6cab..7cd11fe 100644
>> --- a/include/linux/ftrace.h
>> +++ b/include/linux/ftrace.h
>> @@ -484,9 +484,6 @@ static inline void __ftrace_enabled_restore(int enabled)
>>  #ifdef CONFIG_PREEMPT_TRACER
>>    extern void trace_preempt_on(unsigned long a0, unsigned long a1);
>>    extern void trace_preempt_off(unsigned long a0, unsigned long a1);
>> -#else
>> -  static inline void trace_preempt_on(unsigned long a0, unsigned long a1) { }
>> -  static inline void trace_preempt_off(unsigned long a0, unsigned long a1) { }
> 
> If you want to hide the "CALLER_ADDR" for other archs, then simply do:
> 
> # define trace_preempt_on(a0, a1) do { } while (0)
> # define trace_preempt_off(a0, a1) do { } while (0)
> 
> and be done with it.
> 
> Oh, you should add a comment before these defines to the effect of:
> 
>  /*
>   * Use defines instead of static inlines because some arches will make 
>   * code out of the CALLER_ADDR, when we really want these to be a real 
>   * nop.
>   */
> 
> That way, you will document why we use defines instead of static
> inlines.
> 
> -- Steve
> 

Very appreciate your explanation and detailed(even complete) sample code. 
I'll apply your code.

>>  #endif
>>  
>>  #ifdef CONFIG_FTRACE_MCOUNT_RECORD
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 4603b9d..efdd5a0 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -3068,8 +3068,10 @@ void __kprobes add_preempt_count(int val)
>>  	DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=
>>  				PREEMPT_MASK - 10);
>>  #endif
>> +#ifdef CONFIG_PREEMPT_TRACER
>>  	if (preempt_count() == val)
>>  		trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
>> +#endif
>>  }
>>  EXPORT_SYMBOL(add_preempt_count);
>>  
>> @@ -3088,9 +3090,10 @@ void __kprobes sub_preempt_count(int val)
>>  			!(preempt_count() & PREEMPT_MASK)))
>>  		return;
>>  #endif
>> -
>> +#ifdef CONFIG_PREEMPT_TRACER
>>  	if (preempt_count() == val)
>>  		trace_preempt_on(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
>> +#endif
>>  	preempt_count() -= val;
>>  }
>>  EXPORT_SYMBOL(sub_preempt_count);
>> diff --git a/kernel/softirq.c b/kernel/softirq.c
>> index 671f959..e7c8336 100644
>> --- a/kernel/softirq.c
>> +++ b/kernel/softirq.c
>> @@ -112,9 +112,10 @@ static void __local_bh_disable(unsigned long ip, unsigned int cnt)
>>  	if (softirq_count() == cnt)
>>  		trace_softirqs_off(ip);
>>  	raw_local_irq_restore(flags);
>> -
>> +#ifdef CONFIG_PREEMPT_TRACER
>>  	if (preempt_count() == cnt)
>>  		trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
>> +#endif
>>  }
>>  #else /* !CONFIG_TRACE_IRQFLAGS */
>>  static inline void __local_bh_disable(unsigned long ip, unsigned int cnt)
> 
> 
> 

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