Re: [PATCH 00/12 v2] ring-buffer/tracing: Remove disabling of ring buffer while reading trace file

[Steven Rostedt]

On Sat, 21 Mar 2020 19:13:51 +0000
David Laight <David.Laight@xxxxxxxxxx> wrote:

> From: Steven Rostedt
> > Sent: 19 March 2020 23:22  
> ...
> > 
> > This patch series attempts to satisfy that request, by creating a
> > temporary buffer in each of the per cpu iterators to place the
> > read event into, such that it can be passed to users without worrying
> > about a writer to corrupt the event while it was being written out.
> > It also uses the fact that the ring buffer is broken up into pages,
> > where each page has its own timestamp that gets updated when a
> > writer crosses over to it. By copying it to the temp buffer, and
> > doing a "before and after" test of the time stamp with memory barriers,
> > can allow the events to be saved.  
> 
> Does this mean the you will no longer be able to look at a snapshot
> of the trace by running 'less trace' (and typically going to the end
> to get info for all cpus).

I changed patch 9 to be this:

It adds an option "pause-on-trace" that when set, will bring back the
old behavior of pausing recording to the ring buffer when the trace
file is open.

If needed, I can add a kernel command line option and a Kconfig that
makes this set to true by default.

-- Steve