ah, i see what you mean. I think that's an orthogonal property.
Well, it's important in some cases, not that important in other cases.
Historically we've been flip-flopping on that issue in ftrace, whether
it should be coherent by default or not. We had at least three of four
variations of global synchronization. (one was an atomic generation
counter, another variant a global lock)
Eventually people noticed the overhead and asked for it to be faster.
If all you do is to trace high-freq events on all CPUs and you are _not_
interested in the precise interactions, the overhead of global
synchronization can hurt a lot.
In any case, SMP coherency of trace events is an independent property of
the tracer, and preferably something that can be turned on/off.
Ingo
--
