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

> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Minho Ban <mhban@samsung.com>
> ---
> 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

> #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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