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    SubjectRe: Reading EeePC900 battery info causes stalls

    On Sat, 20 Sep 2008, Sitsofe Wheeler wrote:

    > Steven Rostedt wrote:
    > > OK, that is probably the known bug you are hitting. Simply disable the
    > > CONFIG_FTRACE_STARTUP_TEST and you should have the wakeup tracer. The bug is
    > > with the test, not the tracer, so it should not hurt you.
    >
    > Thanks - this made the wakeup tracer appear a you said. I have put two wakeup
    > traces up:
    >
    > http://sucs.org/~sits/test/eeepc-debug/20080920/latency_trace.txt.gz
    > http://sucs.org/~sits/test/eeepc-debug/20080920/trace.txt.gz
    > (each file is around 6Mbytes uncompressed)
    >
    > Here's a small extract of latency_trace.txt:
    >
    > > # tracer: wakeup
    > > #
    > > wakeup latency trace v1.1.5 on 2.6.27-rc6skw-dirty
    > > --------------------------------------------------------------------
    > > latency: 3232905 us, #65620/6180619, CPU#0 | (M:desktop VP:0, KP:0, SP:0

    Peter, these times are crazy, mainly due to the cpu_clock. He probably
    wants to use the sched_clock. Below is a patch to use it instead.

    Sitsofe, I notice that the trace states "desktop". This means that you
    are running with CONFIG_PREEMPT_VOLUNTARY. You want
    CONFIG_PREEMPT.

    [...]
    >
    > Is it intentional that the last event has a time earlier closer to that of the
    > first event?
    >

    Change the config, and see what you get with this patch:

    Note this is not compiled tested:

    ---
    kernel/trace/trace.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    Index: linus.git/kernel/trace/trace.c
    ===================================================================
    --- linus.git.orig/kernel/trace/trace.c 2008-09-20 17:49:00.000000000 -0400
    +++ linus.git/kernel/trace/trace.c 2008-09-20 17:49:35.000000000 -0400
    @@ -60,7 +60,7 @@ ns2usecs(cycle_t nsec)

    cycle_t ftrace_now(int cpu)
    {
    - return cpu_clock(cpu);
    + return sched_clock();
    }

    /*

    -- Steve



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