Re: [LTP] Testing absence of ticks with nohz_full

[Frederic Weisbecker <fweisbec@gmail.com>]

On Mon, Mar 10, 2014 at 11:27:56AM -0400, Steven Rostedt wrote:
> On Mon, 10 Mar 2014 16:17:48 +0100
> Frederic Weisbecker <fweisbec@gmail.com> wrote:
> 
> 
> > On both cases you want to use trace events. So I'd rather suggest you to use perf tools
> > or trace-cmd.
> > 
> > I believe that trace-cmd unfortunately uses per CPU periodic wake up on live
> > recording CPUs so perhaps it's not a good candidate to test isolation. Too bad
> > because kernelshark is cool for an overview.
> 
> Actually, it's not per-cpu. There's a thread per-cpu, but they do not
> need to run on the CPU they monitor. Heck, you can have all threads on
> just one CPU. Actually, they are not threads, they are forked children,
> but you get the idea.

Ah good to know.

> 
> Now that I have wakeup working (with help of irq_work), I should also
> be able to have them only wake if there's something to trace.

Perfect!

> 
> > 
> > Also perf supports some script languages for post processing: python, perl, etc...
> > I think trace-cmd too but rather for custom display of events.
> 
> Yeah, you can write python plugins that will change the display of the
> output. I'm not sure about full integrating with python though.

Ok. So to produce a summary of events with a script maybe perf can do better.
But kernelshark can offer a good overview as well.

So this all depends on what Mats wants to do in the first place: have a tool
which tells you about the noise, which, how much, etc... So post analysis.

Or have a more visual summary.

Thanks.

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