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    SubjectRe: [RFC PATCH 1/2] perf: Enable group siblings on exec if attr::enable_on_exec set
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    On Wed, 2010-11-10 at 22:17 +0800, Lin Ming wrote:
    > On Wed, 2010-11-10 at 20:19 +0800, Peter Zijlstra wrote:
    > > On Wed, 2010-11-10 at 14:15 +0800, Lin Ming wrote:
    > > > Currently, only group leader is enabled on exec.
    > >
    > > That's enough, right? If all sibling events are already enabled enabling
    > > the group leader makes the whole thing go.
    >
    > No.
    >
    > If the event group is disabled by default("perf stat" case) and will be
    > enabled at next exec, then actually only the group leader will be
    > enabled , because all siblings are explicitly disabled(->state ==
    > PERF_EVENT_STATE_OFF). So the siblings will never be enabled.

    Right, so what I was saying is, don't disable all the siblings by
    default, so that only the group leader will be disabled. In that case
    nothing will get scheduled because the group leader is not enabled.

    So: {disabled, enabled, enabled} will not actually get scheduled and the
    group as a whole is effectively disabled. Once the enabled_on_exec flips
    the group leader to 'enabled' the whole group becomes enabled.

    I don't mind the patch too much (although I would like to avoid that
    double sibling iteration in both group_enable_on_exec() and
    __perf_event_mark_enabled()), but I think it can already work as is.




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