Re: [RFC][PATCH] ring-buffer: Have nested events still record running time stamp

[Mathieu Desnoyers]

----- On Jun 25, 2020, at 9:44 AM, rostedt rostedt@xxxxxxxxxxx wrote:

> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> 
> [ SEVEN YEAR PROBLEM SOLVED! ]
> 
> Up until now, if an event is interrupted while it is recorded by an
> interrupt, and that interrupt records events, the time of those events will
> all be the same. This is because events only record the delta of the time
> since the previous event (or beginning of a page), and to handle updating
> the time keeping for that of nested events is extremely racy. After years of
> thinking about this and several failed attempts, I finally have a solution
> to solve this puzzle.

Out of curiosity, considering that LTTng has solved this problem 10+ years ago
with a simpler concurrency-friendly time-stamping model, why not simply use it
rather than add complexity to the current ftrace timestamp scheme ?

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com