linux-kernel - Re: [PATCH v2 2/2] tracing: kdb: Allow ftdump to skip all but the last few lines

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Message-ID: <20190313094701.06b4e93d@gandalf.local.home>
Date:   Wed, 13 Mar 2019 09:47:01 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        Brian Norris <briannorris@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] tracing: kdb: Allow ftdump to skip all but the
 last few lines

On Tue, 12 Mar 2019 23:25:28 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri,  8 Mar 2019 11:32:05 -0800
> Douglas Anderson <dianders@...omium.org> wrote:
> 
> > The 'ftdump' command in kdb is currently a bit of a last resort, at
> > least if you have lots of traces turned on.  It's going to print a
> > whole boatload of lines out your serial port which is probably running
> > at 115200.  This could easily take many, many minutes.
> > 
> > Usually you're most interested in what's at the _end_ of the ftrace
> > buffer, AKA what happened most recently.  That means you've got to
> > wait the full time for the dump.  The 'ftdump' command does attempt to
> > help you a little bit by allowing you to skip a fixed number of lines.
> > Unfortunately it provides no way for you to know how many lines you
> > should skip.
> > 
> > Let's do similar to python and allow you to use a negative number to
> > indicate that you want to skip all lines except the last few.  This
> > allows you to quickly see what you want.  
> 
> Why not just read how many entries are in the ring buffer and return that?
> 
> 	cnt = 0;
> 	for_each_cpu(cpu, tr->tracing_cpumask)
> 		cnt += ring_buffer_entries_cpu(tr->trace_buffer, cpu);
> 	return cnt;
> 
> The output will print out one entry per line.
> 

Note, I pulled in patch 1 into my queue. So you only need to resend
this patch.

-- Steve