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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.32-2
    Ingo Molnar wrote:
    ...

    > i've implemented the 'tracing follows the task' logic in the -32-2
    > patch, available from the usual place:
    >
    > http://redhat.com/~mingo/realtime-preempt/
    >
    > i've also added a CPU# field and i've reworked latency_trace format, to
    > make it more readable. Whenever preempt_wakeup_timing is enabled,
    > user-tracing will follow the traced task, if it's disabled then tracing
    > will stay on the CPU. No other changes.
    ...
    > Ingo

    On my machine, disabling CONFIG_LATENCY_TRACE causes the kernel to stop
    reporting preempt latencies. After
    # echo 1 > /proc/sys/kernel/preempt_max_latency

    /proc/sys/kernel/preempt_max_latency always shows 1 no matter what load
    is on the machine. I´ve seen this behavior since the first time I tried
    to disable CONFIG_LATENCY_TRACE, around V0.7.31.something.

    Below is the exact diff between the 2 configs (the one that shows
    latencies and the one that doesn´t). Note that the only intentional
    change is turning off CONFIG_LATENCY_TRACE.
    =======================================================
    --- /tmp/config-2.6.10-rc2-mm3-V0.7.32-2.lat 2004-12-07
    16:25:03.000000000 +0200
    +++ /tmp/config-2.6.10-rc2-mm3-V0.7.32-2.no_lat 2004-12-07
    11:06:19.000000000 +0200
    @@ -1,7 +1,7 @@
    #
    # Automatically generated make config: don't edit
    # Linux kernel version: 2.6.10-rc2-mm3-V0.7.32-2
    -# Tue Dec 7 11:07:07 2004
    +# Mon Dec 6 20:24:09 2004
    #
    CONFIG_X86=y
    CONFIG_MMU=y
    @@ -137,6 +137,7 @@
    CONFIG_MTRR=y
    # CONFIG_EFI is not set
    CONFIG_HAVE_DEC_LOCK=y
    +# CONFIG_REGPARM is not set

    #
    # Performance-monitoring counters support
    @@ -1711,12 +1712,12 @@
    CONFIG_CRITICAL_IRQSOFF_TIMING=y
    CONFIG_CRITICAL_TIMING=y
    CONFIG_LATENCY_TIMING=y
    -CONFIG_LATENCY_TRACE=y
    -CONFIG_MCOUNT=y
    +# CONFIG_LATENCY_TRACE is not set
    # CONFIG_RT_DEADLOCK_DETECT is not set
    # CONFIG_DEBUG_KOBJECT is not set
    CONFIG_DEBUG_BUGVERBOSE=y
    # CONFIG_DEBUG_INFO is not set
    +CONFIG_USE_FRAME_POINTER=y
    CONFIG_FRAME_POINTER=y
    CONFIG_EARLY_PRINTK=y
    # CONFIG_DEBUG_STACKOVERFLOW is not set
    =======================================================
    --
    Eran Mann
    -
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