linux-kernel - Re: [PATCH 2/5] ftrace: infrastructure for supporting binary record

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Message-ID: <20090119213720.GF690@ghostprotocols.net>
Date:	Mon, 19 Jan 2009 19:37:21 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] ftrace: infrastructure for supporting binary record

Em Mon, Jan 19, 2009 at 10:08:40PM +0100, Frederic Weisbecker escreveu:
> On Mon, Jan 19, 2009 at 06:25:23PM -0200, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Jan 19, 2009 at 08:28:03PM +0100, Frédéric Weisbecker escreveu:
> > > 2009/1/2 Arnaldo Carvalho de Melo <acme@...stprotocols.net>:
> > > >
> > > > warning: I haven't looked at the patch details
> > > >
> > > > But I would love to use something like this to provide the exact
> > > > contents the userspace blktrace utilities want.
> > > >
> > > > - Arnaldo
> > > >
> > > 
> > > 
> > > Hi Arnaldo,
> >  
> > > Since you talked about binary record for the blk tracer, I just recall
> > > this patch.  Are you sure this infrastructure would cover your needs?
> > 
> > Nope, now that I look at it it definetely isn't what I need. See? the
> > warning was valid after all :-)
> > 
> > What I want and will experiment now is to almost dump the contents of
> > the ring buffer as-is to userspace. I want that so that I can use
> > blkparse to validate the ring buffer + blkFtrace routines produced
> > buffer.
> > 
> > So probably it will be a matter of using trace_iter to signal that, and
> > when it gets to my print_line routine I just put together the initial
> > trace format expected by blkparse + the ones I'm collecting at
> > tracepoint time.
> 
> 
> So you would like two different trace files? Or print both bin and formatted
> output together in the same file?
> I'm not sure I understand :-s

output depends on iter_flags, most of what is needed is there, but I
guess there are too many ways to achieve the same result and some
keywords that are already used for other purposes, such as
TRACE_ITER_BIN -> print_bin_fmt that forces all traces to first have
pid, cpu and timestamp (all using trace_seq_putmem), then whatever the
tracer wants to put after that (if it registered a tracer_event _and_ it
has a ->binary() emitter), when I wanted it to just call ->binary(),
where I would emulate exactly the old blktrace format, then we would be
able to just ask for binary traces, collect them thru
/d/tracing/trace_pipe and pipe them into blkparse for
validation/debugging the ring_buffer + ftrace + blkFtrace code.

I'll try to get a brain dump in the form of working code later
today/early tomorrow, now I'm being preempted by my wife to do those
social things like having dinner and going to the movie theater 8)

Regards,

- Arnaldo
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