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    SubjectRe: [PATCHv2 00/25] perf tool: Add support for multiple data file storage
    On 9/9/13 9:06 AM, Ingo Molnar wrote:
    >> Aren't you losing potentially important events by doing that -- FORK,
    >> COMM, MMAP?
    >
    > I suspect these could/should be tracked and emitted fully (in bulk) when a
    > new data file is opened, so that each partial data file is fully
    > consistent?

    In my case I am not saving task events, but processing them. In Jiri's
    case where events are written to a file it should be possible to stash
    the unprocessed events on a list, when the exit happens move them to a
    dead threads list which can be cleaned up from time to time and then on
    file dump requests dump the task events followed by the sample events.

    >
    >> I have a flight recorder style command that address this problem
    >> (long-running/daemons) by processing task events and then stashing the
    >> sample events on a time-ordered list with chopping to maintain the time
    >> window.
    >
    > Could this be used to emit currently relevant task context?

    sure.

    >
    > Btw., I also think it would be useful to have kernel support for that -
    > the 'collections' stuff I talked about a good while ago: the kernel would
    > work with user-space to iterate over all MMAPs and all running COMMs at
    > the opening of a tracing session.
    >
    > That way we could avoid racy access to /proc, we could make sure that all
    > information that is emitted by FORK/COMM/MMAP is also emitted for the
    > 'bulk' data, etc.

    Walking the task list and emitting events would be better but wouldn't
    that be a performance hit holding the task lock (tasklist_lock?)? (I
    thought that one is needed when walking the task list.)

    David



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