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    Subject[RFC/PATCH] Prevent wasting time to find out get_parent_ip
    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.

    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) { }
    #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)
    --
    1.7.5.4


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