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

    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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