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    SubjectRe: 2.6.15-rt4 failure with LATENCY_TRACE on x86_64
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    On Thu, 2006-01-12 at 16:07 -0600, Clark Williams wrote:
    > Ingo/Steve,
    >
    > Did I miss a "Don't turn on latency tracing for x86_64" message
    > somewhere?
    >
    > I'm seeing a failure on my Athlon64 3000+ where, when I turn on
    > CONFIG_LATENCY_TRACE, the init program segfaults. Doesn't happen with a
    > statically linked shell like sash (e.g. init=/sbin/sash boots ok), but
    > if /sbin/init or /bin/sh is used, the init program segfaults. Presumably
    > any dynamically linked program will fail.
    >
    > Attached is console output for a boot failure (segfault messages
    > truncated after four lines, since they're all the same) as well as the
    > config files for both working and failing kernels.
    >
    > I'm not sure where to start looking on this one. Barring any advise, I'm
    > going to look for occurrences of CONFIG_LATENCY_TRACE, especially in
    > proximity to exec.

    OK, I'm actually sending you this email on a x86_64 running
    2.6.15-rt4-sr2, with latency tracing on. But unfortunately, I have a
    AMD X2 that each core has it's own tsc counter that is not in sync, and
    since the latency tracer uses tsc, I get garbage. But beware, the tsc
    does slow down when the cpu idles, so it gives bad results even for non
    x2 systems.

    I finally was able to boot this with using the PM timer, but the
    beginning of my dmesg is still filled with:

    read_tsc: ACK! TSC went backward! Unsynced TSCs?

    Have you tried booting with idle=poll? I wonder if that would help?

    -- Steve


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