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    SubjectRe: [RFC,PATCH 2/2] perf, x86: Utilize the LBRs for machine/oops debugging

    * Peter Zijlstra <peterz@infradead.org> wrote:

    > On Mon, 2010-03-29 at 19:02 +0200, Ingo Molnar wrote:
    >
    > > Plus, it would be nice to have a sysctl entry for this as well - so that
    > > production systems can enable this if they want to enrich the output of
    > > some difficult-to-analyze kernel crash, without yet another reboot.
    >
    > Right, could do, but once it crashed it clearly to late to enable anything
    > ;-)

    No. What i mean is that with your patch, a debugging session would go like
    this:

    < kernel crashes > # reboot #1

    < admin logs in and scratches head >
    < admin consults kernel hackers and enables lbr_debug=1 in /etc/grub.conf >

    < admin reboots > # reboot #2

    < kernel crashes again > # reboot #3

    With the sysctl we'd have one reboot less:

    < kernel crashes > # reboot #1

    < admin logs in and scratches head >
    < admin consults kernel hackers and tweaks /proc/sys/kernel/x86/lbr_debug >

    < kernel crashes again > # reboot #2

    Thanks,

    Ingo


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