linux-kernel - Re: [RFD] Future tracing/instrumentation directions

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Date:	Thu, 20 May 2010 12:07:34 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@....de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	Robert Richter <robert.richter@....com>
Subject: Re: [RFD] Future tracing/instrumentation directions

On Thu, May 20, 2010 at 11:31:31AM +0200, Ingo Molnar wrote:
>  - [ While it's still a long way off, if this trend continues
>      we eventually might even be able to get rid of the 
>      /debug/tracing/ temporary debug API and get rid of 
>      the ugly in-kernel pretty-printing bits. This is 
>      good: it may make Andrew very happy for a change ;-)
> 
>      The main detail here to be careful of is that lots of
>      people are fond of the simplicity of the 
>      /debug/tracing/ debug UI, so when we replace it we 
>      want to do it by keeping that simple workflow (or 
>      best by making it even simpler). I have a few ideas 
>      how to do this.



How? We can emulate the /debug/tracing result with something
like perf trace, still that won't replace the immediate
availability of the result of any trace, which makes it
valuable for any simplest workflows.




> Regarding performance and complexity, which is our main 
> worry atm, fortunately there's work going on in that 
> direction - please see PeterZ's recent string of patches 
> on lkml:
> 
>   4f41c01: perf/ftrace: Optimize perf/tracepoint interaction for single events
>   a19d35c: perf: Optimize buffer placement by allocating buffers NUMA aware
>   ef60777: perf: Optimize the perf_output() path by removing IRQ-disables
>   fa58815: perf: Optimize the hotpath by converting the perf output buffer to local_t



I would like to highlight the following commit too that _totally_
changes the requirements of our next common ring buffer, whatever it is: 

    c792061: perf: Disallow mmap() on per-task inherited events

Now we only need to care about local contention, we have removed the
support for buffers that contend across cpus in a single process.

Do I understand it right?



> 3) Add the function-tracer and function-graph tracer
>    as an event and integrate it into perf.
> 
>    This will live-test the efficiency of the unification
>    and brings over the last big ftrace plugin to perf.


I may start to take care of this soon.

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