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    SubjectRe: [PATCH -tip, final] perf, x86: Add hw_watchdog_set_attr() in a sake of nmi-watchdog on P4

    * Cyrill Gorcunov <> wrote:

    > perf, x86: P4 PMU - Add hw_watchdog_set_attr helper to simulate cpu-cycles counting in nmi-watchdog
    > Because of constraints existed in Netburst PMU counting
    > cpu cycles is allowed for one consumer only.
    > If the kernel is booted up with nmi-watchdog enabled
    > the watchdog become a consumer of such event and there
    > is no more room left for "perf top" and friends (ie any
    > attempts to count cpu cycles simultaneously with nmi-watchdog
    > doomed to fail).

    Hm, what is the symptom - 'perf top' reports nothing?

    If multiple users request cycles then perf will time-share them -
    this is what happens if you run many 'perf top' or 'perf stat'
    sessions in parallel for example. For example i just tried to run six
    separate 'perf top' in parallel - and all six worked fine.

    So the question is, why does the NMI watchdog prevent 'perf top' from
    working on a P4?



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