Messages in this thread | | | Subject | Re: [PATCH] ftrace: use a global counter for the global clock | From | Valdis.Kletnieks@vt ... | Date | Fri, 16 Sep 2011 17:14:53 -0400 |
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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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