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From: David Laight <David.Laight@ACULAB.COM>
To: 'Steven Rostedt' <rostedt@goodmis.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	"Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
	Peter Wu <peter@lekensteyn.nl>, Jonathan Corbet <corbet@lwn.net>,
	Tom Zanussi <zanussi@kernel.org>,
	"Shuah Khan" <shuahkhan@gmail.com>, bpf <bpf@vger.kernel.org>
Subject: RE: [PATCH 00/12 v2] ring-buffer/tracing: Remove disabling of ring buffer while reading trace file
Date: Fri, 27 Mar 2020 10:07:00 +0000
Message-ID: <60977a309b5d46979a9a9bbd46c10932@AcuMS.aculab.com> (raw)
In-Reply-To: <20200326214617.697634f3@oasis.local.home>

From: Steven Rostedt
> Sent: 27 March 2020 01:46
> On Sat, 21 Mar 2020 19:13:51 +0000
> David Laight <David.Laight@ACULAB.COM> 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.

Maybe a different file 'trace_no_pause' ?
Along with the one that lets you read the raw trace and get EOF.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


  reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-19 23:22 Steven Rostedt
2020-03-19 23:22 ` [PATCH 01/12 v2] selftest/ftrace: Fix function trigger test to handle trace not disabling the tracer Steven Rostedt
2020-03-19 23:22 ` [PATCH 02/12 v2] tracing: Save off entry when peeking at next entry Steven Rostedt
2020-03-20  2:57   ` Masami Hiramatsu
2020-03-26  9:12   ` [tracing] cd8f62b481: BUG:sleeping_function_called_from_invalid_context_at_mm/slab.h kernel test robot
2020-03-19 23:22 ` [PATCH 03/12 v2] ring-buffer: Have ring_buffer_empty() not depend on tracing stopped Steven Rostedt
2020-03-19 23:22 ` [PATCH 04/12 v2] ring-buffer: Rename ring_buffer_read() to read_buffer_iter_advance() Steven Rostedt
2020-03-19 23:22 ` [PATCH 05/12 v2] ring-buffer: Add page_stamp to iterator for synchronization Steven Rostedt
2020-03-19 23:22 ` [PATCH 06/12 v2] ring-buffer: Have rb_iter_head_event() handle concurrent writer Steven Rostedt
2020-03-19 23:22 ` [PATCH 07/12 v2] ring-buffer: Do not die if rb_iter_peek() fails more than thrice Steven Rostedt
2020-03-19 23:22 ` [PATCH 08/12 v2] ring-buffer: Optimize rb_iter_head_event() Steven Rostedt
2020-03-19 23:22 ` [PATCH 09/12 v2] ring-buffer: Do not disable recording when there is an iterator Steven Rostedt
2020-03-19 23:22 ` [PATCH 10/12 v2] tracing: Do not disable tracing when reading the trace file Steven Rostedt
2020-03-19 23:22 ` [PATCH 11/12 v2] ring-buffer/tracing: Have iterator acknowledge dropped events Steven Rostedt
2020-03-19 23:22 ` [PATCH 12/12 v2] tracing: Have the document reflect that the trace file keeps tracing enabled Steven Rostedt
2020-03-21 19:13 ` [PATCH 00/12 v2] ring-buffer/tracing: Remove disabling of ring buffer while reading trace file David Laight
2020-03-22 18:07   ` Steven Rostedt
2020-03-27  1:46   ` Steven Rostedt
2020-03-27 10:07     ` David Laight [this message]
2020-03-27 14:30       ` Steven Rostedt
2020-03-27 14:56         ` David Laight

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