linux-kernel - Re: [RFC PATCH 0/4] perf: Custom contexts

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Date:	Mon, 14 Mar 2011 23:43:46 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
Subject: Re: [RFC PATCH 0/4] perf: Custom contexts

On Mon, Mar 14, 2011 at 06:56:03PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Mar 14, 2011 at 10:20:53PM +0100, Frederic Weisbecker escreveu:
> > On Mon, Mar 14, 2011 at 06:03:15PM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Mon, Mar 14, 2011 at 09:51:02PM +0100, Frederic Weisbecker escreveu:
> > > > On Mon, Mar 14, 2011 at 05:43:41PM -0300, Arnaldo Carvalho de Melo wrote:
> 
> > > But starter on a starter? Couldn't grok, could you provide an example?
> > 
> > I have no strong example in mind.
> > 
> > But one may want to count instructions when we are in an interrupt and
> > lock A is held.
> 
> Those would be and/or starter/stopper expressions, something like:
> 
> $ perf record -e instructions@(irq:irq_handler_entry(irq=eth0) && lock:lock_acquired(foo_lock))..irq:irq_handler_exit(\1) \
> 	      -e instructions \
> 	netperf
> 
> when all starters before the stopper are valid, we entered a range.

So, if we want to stop when lock is released, we do:

perf record -e instructions@(irq:irq_handler_entry(irq=eth0) && lock:lock_acquired(foo_lock))..lock:lock_release(foo_lock) && irq:irq_handler_exit(\1) \
             -e instructions \
	netperf

Or || for stoppers like you do below? Hmm, I'm confused...

>  
> > Or count instruction when A and B are held.
> 
> Using wildcards that matches just the things we want to make it a bit
> more compact:
> 
> $ perf record -e inst*@(irq:*entry(irq=eth0) && lock:*acquired(A) && \
> 			lock:*acquired(B))..(lock:*release(A) || lock:*release(B)) \
> 	./my_workload
> 
> Parenthesis don't have to be used just for filters :) Just like in C,
> they can be used to express the list of parameters for a function or for
> expressions, etc.

The && make sense. But the || ?

What about:

-e inst*@(lock:*acquire(A)..lock:*release(A))@(lock:*acquire(B)..lock:*release(B))@(irq:*entry(irq=eth0)..irq:*exit(irq=eth0))

That looks to me less confusing.


> 
> > Or count instruction in page faults happening in read() syscall.
> 
> We would need to use 'perf probe' first to insert the entry and exit
> probes on the page fault handling path:
> 
> [root@...icio ~]# perf list *fault* *:*fault*
> 
> List of pre-defined events (to be used in -e):
>   page-faults OR faults                      [Software event]
>   minor-faults                               [Software event]
>   major-faults                               [Software event]
>   alignment-faults                           [Software event]
>   emulation-faults                           [Software event]
> 
>   kvm:kvm_page_fault                         [Tracepoint event]
> [root@...icio ~]#
> 
> But then an expression could be used like I showed above for the
> previous use case you mentioned.

Right.

> 
> > Event range define a state, and anytime you need to profile/trace a
> > desired stacked state, starters on starters can be a good solution,
> > thus even a common practice.
> 
> See above, is that what you're thinking about?

I'm not sure. I can find the meaning of && in your expressions. But not
the meaning of ||. I lack some sleep though :)

But still, I'm all for trying to make a better and smarter way to
express these events, following your suggestions, but I'm not sure I have
the motivation to write a full parser capable of evaluating near C expressions.
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