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Date: Sat, 27 Sep 2008 20:42:12 +0200 From: Ingo Molnar <mingo@...e.hu> To: Steven Rostedt <rostedt@...dmis.org> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Martin Bligh <mbligh@...gle.com>, Peter Zijlstra <peterz@...radead.org>, Martin Bligh <mbligh@...igh.org>, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Andrew Morton <akpm@...ux-foundation.org>, prasad@...ux.vnet.ibm.com, Mathieu Desnoyers <compudj@...stal.dyndns.org>, "Frank Ch. Eigler" <fche@...hat.com>, David Wilder <dwilder@...ibm.com>, hch@....de, Tom Zanussi <zanussi@...cast.net>, Steven Rostedt <srostedt@...hat.com> Subject: Re: [RFC PATCH 1/3] Unified trace buffer * Steven Rostedt <rostedt@...dmis.org> wrote: > > On Sat, 27 Sep 2008, Ingo Molnar wrote: > > > > 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. > > Just a note. The current ring buffering system that I'm proposing > keeps its own time stamp counter (currently sched_clock) that will > most likely be updated later. I'm trying to keep this ring buffer > system as dumb as possible. It does not even implement the merge sort. > That's up to the tracer to handle. There's nothing stopping the trace > from adding some atomic counter to each event to help it sort. correct. The price is all the notifier/callback overhead and the loss of type checking of the record contents. But that's an unavoidable price of abstraction, at least in C. > So yes, the tracer can implement anything it wants on top of the ring > buffer ;-) yes, very nice! :) Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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