Re: perf_counters issue with enable_on_exec

[stephane eranian <eranian@googlemail.com>]

On Mon, Aug 24, 2009 at 11:35 PM, Paul Mackerras<paulus@samba.org> wrote:
> stephane eranian writes:
>
>> I am running into an issue trying to use enable_on_exec
>> in per-thread mode with an event group.
>>
>> My understanding is that enable_on_exec allows activation
>> of an event on first exec. This is useful for tools monitoring
>> other tasks and which you invoke as: tool my_program. In
>> other words, the tool forks+execs my_program. This option
>> allows developers to setup the events after the fork (to get
>> the pid) but before the exec(). Only execution after the exec
>> is monitored. This alleviates the need to use the
>> ptrace(PTRACE_TRACEME) call.
>>
>> My understanding is that an event group is scheduled only
>> if all events in the group are active (disabled=0). Thus, one
>
> Not quite - if the leader is disabled then none of the group goes on.
> If the leader is enabled then it and any other group members that are
> enabled go on.  If a non-leader member is disabled then it doesn't go
> on but it doesn't stop other members from going on.
>
okay, what is not clear to me is why you need that level of granularity?