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It only needs to be unique per pid doesn't it? Is it possible to have many threads writing into the same ring buffer in that scenario ? Are all event records stamped with their associated PID ? As long as we have enough information to know which thread was associated with the timestamp cookie on both ends (request for callchain and saving the user callchain on return to userspace), we should be OK. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com