From: Steven Rostedt <rostedt@goodmis.org>
To: David Laight <David.Laight@ACULAB.COM>
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: Sun, 22 Mar 2020 14:07:56 -0400 [thread overview]
Message-ID: <20200322140756.7257b867@gandalf.local.home> (raw)
In-Reply-To: <2a7f96545945457cade216aa3c736bcc@AcuMS.aculab.com>
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).
If there's a use case for this, it will be trivial to add an option to
bring back the old behavior. If you want that, I can do that, and even add
a config that makes it the default.
>
> A lot of the time trace is being written far too fast for it to make
> any sense to try to read it continuously.
>
> Also, if BPF start using ftrace, no one will be able to use it for
> 'normal debugging' on such systems.
I believe its used for debugging bpf, not for normal tracing. BPF only
uses this when it has their trace_printk() using it. Which gives that nasty
"THIS IS A DEBUG KERNEL" message ;-) Thus, I don't think you need to
worry about bpf having this in production.
-- Steve
next prev parent reply other threads:[~2020-03-22 18:08 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-19 23:22 [PATCH 00/12 v2] ring-buffer/tracing: Remove disabling of ring buffer while reading trace file 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
[not found] ` <20200326091256.GR11705@shao2-debian>
2020-04-01 14:07 ` [tracing] cd8f62b481: BUG:sleeping_function_called_from_invalid_context_at_mm/slab.h Masami Hiramatsu
2020-04-01 14:21 ` Steven Rostedt
2020-04-01 15:04 ` Steven Rostedt
2020-04-02 7:19 ` Masami Hiramatsu
2020-04-02 18:14 ` Steven Rostedt
2020-04-03 6:47 ` Masami Hiramatsu
2020-04-03 13:16 ` Steven Rostedt
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 [this message]
2020-03-27 1:46 ` Steven Rostedt
2020-03-27 10:07 ` David Laight
2020-03-27 14:30 ` Steven Rostedt
2020-03-27 14:56 ` David Laight
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