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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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