Hi Mathieu, On Fri, May 09, 2025 at 08:23:49AM -0400, Mathieu Desnoyers wrote: > On 2025-05-08 14:54, Steven Rostedt wrote: > > On Thu, 8 May 2025 14:49:59 -0400 > > Mathieu Desnoyers <mathieu.desnoy...@efficios.com> wrote: > > > > > AFAIR, the cookie method generates the cookie by combining the cpu > > > number with a per-cpu count. > > > > > > This ensures that there are not two cookies emitted at the same time > > > from two CPUs that have the same value by accident. > > > > > > How would the timestamp method prevent this ? > > > > Do we care? 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.
Yep, basically perf sets PERF_SAMPLE_TID (and sample_id_all) which makes every records come with PID/TID.. Thanks, Namhyung
