Re: [PATCH] ftrace: use a global counter for the global clock

[Valdis.Kletnieks@vt.edu]

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On Fri, 16 Sep 2011 08:18:26 EDT, Steven Rostedt said:

> +	return atomic64_add_return(1, &trace_counter);

Given that the usefulness of this is probably directly proportional to the
number of cores on the box, is this subject to cache line ping-ponging on
systems with many cores?

> When debugging tight race conditions, it can be helpful to have a
> synchronized tracing method. Although in most cases the global clock
> provides this functionality, if timings is not the issue, it is more
> comforting to know that the order of events really happened in a precise
> order.

One wonders if the overhead can end up being enough to change the
ordering, and possibly cause a heisenbug (most likely if the race condition
involves one CPU doing something we're tracing, and another CPU doing
something we are *not* tracing)...

If that's considered not an issue, feel free to stick this on it:
Reviewed-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>



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