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    SubjectRe: [PATCH 1/2] tracing: convert trace_clock_local() as weak function
    On Fri, Oct 16, 2009 at 07:38:24PM +0800, Wu Zhangjin wrote:
    >trace_clock_local() is based on the arch-specific sched_clock(), in X86,
    >it is tsc(64bit) based, which can give very high precision(about 1ns
    >with 1GHz). but in MIPS, the sched_clock() is jiffies based, which can
    >give only 10ms precison with 1000 HZ. which is not enough for tracing,
    >especially for Real Time system.
    >so, we need to implement a MIPS specific sched_clock() to get higher
    >precision. There is a tsc like clock counter register in MIPS, whose
    >frequency is half of the processor, so, if the cpu frequency is 800MHz,
    >the time precision reaches 2.5ns, which is very good for tracing, even
    >for Real Time system.
    >but 'Cause it is only 32bit long, which will rollover quickly, so, such
    >a sched_clock() will bring with extra load, which is not good for the
    >whole system. so, we only need to implement a arch-specific
    >trace_clock_local() for tracing. as a preparation, we convert it as a
    >weak function.
    >The MIPS specific trace_clock_local() is coming in the next patch.
    >Signed-off-by: Wu Zhangjin <>
    > kernel/trace/trace_clock.c | 2 +-
    > 1 files changed, 1 insertions(+), 1 deletions(-)
    >diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
    >index 20c5f92..a04dc18 100644
    >--- a/kernel/trace/trace_clock.c
    >+++ b/kernel/trace/trace_clock.c
    >@@ -26,7 +26,7 @@
    > * Useful for tracing that does not cross to other CPUs nor
    > * does it go through idle events.
    > */
    >-u64 notrace trace_clock_local(void)
    >+u64 __attribute__((weak)) notrace trace_clock_local(void)

    We have __weak.

    > {
    > unsigned long flags;
    > u64 clock;
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