Messages in this thread | | | Date | Sun, 26 Oct 2008 07:25:56 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2][RFC] ftrace: function oprofiler |
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On Sun, Oct 26, 2008 at 09:58:01AM -0400, Steven Rostedt wrote: > > On Sun, 26 Oct 2008, Peter Zijlstra wrote: > > > On Sat, 2008-10-25 at 20:55 -0400, Steven Rostedt wrote: > > > > > This is a function profiler to count the number of times a function is hit. > > > > I have to ask, _why_? > > > > It seems like a nice enough gimmick, but is this information actually > > useful? > > Well, it does let you know for sure which functions are the hottest paths. > Perhaps you have a "slow path" function. This will show you how slow > that slow path is. That is, how many times it is hit compared to the > fast path.
And the ratio between the "hot path" and the "slow path" can be very helpful in working out what sorts of optimizations can be used. Is a give optimization that gains a factor of ten on the hot path and loses a factor of 50 on the slow path a win?
Of course, you also need some estimate of the cost of the hot paths and the slow paths.
Thanx, Paul
> With dynamic ftrace, you can also pick and choose which functions > are to be counted. > > What is also nice about it (and something that I will use it for), is that > it will show you the functions that will be hit the most during a trace. > If you do not care about those functions, then you can easily filter them > out for your trace. > > This patch is also a proof of concept. I'm sure others can think of more > useful things to do by adding more stuff to this patch.
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