Re: [RFD] Future tracing/instrumentation directions

From: Frederic Weisbecker
Date: Thu May 20 2010 - 06:07:35 EST

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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