linux-kernel - Re: [PATCH v6 3/3] tracing: kdb: Allow ftdump to skip all but the last few entries

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Message-ID: <20190320105028.6t6urpf344mljb2g@holly.lan>
Date:   Wed, 20 Mar 2019 10:50:28 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net,
        Brian Norris <briannorris@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 3/3] tracing: kdb: Allow ftdump to skip all but the
 last few entries

On Tue, Mar 19, 2019 at 10:12:06AM -0700, Douglas Anderson 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 data 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
> entries.  Unfortunately it provides no way for you to know how many
> entries 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 entries except the last few.  This
> allows you to quickly see what you want.
> 
> Note that we also change the printout in ftdump to print the
> (positive) number of entries actually skipped since that could be
> helpful to know when you've specified a negative skip count.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
> Changes in v6:
> - Keep tracing disabled between counting and dumping.
> - Remove Daniel Thompson Ack due to changes between v5 and v6.

... and I'm very happy to replace it:
Acked-by: Daniel Thompson <daniel.thompson@...aro.org>


Daniel.