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    SubjectRe: [PATCH 3/6] perf record: add time-of-day option


    On 03/03/2011 01:51 AM, Ingo Molnar wrote:
    >
    > * David Ahern <daahern@cisco.com> wrote:
    >
    >>> How does all that deal with CLOCK_REALTIME being affected by NTP and
    >>> settimeofday? Not really, as far as I can tell. It somehow works, but
    >>> that depends on the frequency of your event injection.
    >>
    >> It is sampled at some periodic rate to get NTP changes. Right now it is
    >> hardcoded at once an hour. The frequency option can be added to the
    >> --tod parameter.
    >
    > As Thomas mentioned, we probably need something more complete than that.

    Just responded to Thomas' email with a simpler proposal than munging on
    tracepoints and trying to track time-of-day implicitly.

    > Still your approach is obviously useful and i'd like to stress that explicitly. Have

    Thanks for stating that.

    > you considered another related feature, feeding printk lines as special 'string
    > events' into the perf ringbuffer?
    >
    > It would round up your scheme very nicely: that way you'd have a single, global,
    > GTOD-correlated event store/flow for basically every system event you might be
    > interested in. You could switch events (and tracepoints) on/off based on need,
    > controlling the type and rate of information in a very finegrained way.
    >
    > If the printk approach works out i'd even suggest that such a facility would need a
    > separate tool within perf: 'perf syslog' or 'perf log'. It would heavily reuse
    > perf-script and other perf internal facilities, obviously - but you would not be
    > tied to any particular sub-tool implementation.
    >
    > EDAC type events could feed into this as well, giving the tool a broader 'system
    > health' aspect as well, beyond the 'system performance analysis' aspect.

    I can look into it (as time allows) once I get the dumping of software
    events done.

    David

    >
    > Thanks,
    >
    > Ingo


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