linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Steven Rostedt <rostedt@goodmis.org>
To: Claudio <claudio.fontana@gliwa.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org
Subject: Re: ftrace global trace_pipe_raw
Date: Tue, 24 Jul 2018 10:25:06 -0400	[thread overview]
Message-ID: <20180724102506.42114a68@gandalf.local.home> (raw)
In-Reply-To: <20180724102316.41cdb8a1@gandalf.local.home>

On Tue, 24 Jul 2018 10:23:16 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> > 
> > Would work in the direction of adding a global trace_pipe_raw be considered
> > for inclusion?  
> 
> The design of the lockless ring buffer requires not to be preempted,
> and that the data cannot be written to from more than one location. To
> do so, we make a per CPU buffer, and disable preemption when writing.
> This means that we have only one writer at a time. It can handle
> interrupts and NMIs, because they will finish before they return and
> this doesn't break the algorithm. But having writers from multiple CPUs
> would require locking or other heaving synchronization operations that
> will greatly reduce the speed of writing to the buffers (not to mention
> the cache thrashing).

And why would you need a single buffer? Note, we are working on making
libtracecmd.so that will allow applications to read the buffers and the
library will take care of the interleaving of the raw data. This should
hopefully be ready in about three months or so.

-- Steve

  reply	other threads:[~2018-07-24 14:25 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-06  6:22 ftrace performance (sched events): cyclictest shows 25% more latency Claudio
2018-07-06 21:24 ` Steven Rostedt
2018-07-06 21:39   ` Steven Rostedt
2018-07-06 22:00     ` Steven Rostedt
2018-07-09 10:06   ` Claudio
2018-07-09 14:53     ` Claudio
2018-07-09 15:11       ` Steven Rostedt
2018-07-09 15:32 ` Steven Rostedt
2018-07-24  9:58   ` ftrace global trace_pipe_raw Claudio
2018-07-24 14:23     ` Steven Rostedt
2018-07-24 14:25       ` Steven Rostedt [this message]
2018-07-24 15:30         ` Claudio
2018-12-19 11:32       ` Claudio
2018-12-19 16:37         ` Steven Rostedt
2019-01-16  8:00           ` Claudio
2019-01-16 13:47             ` Steven Rostedt
2018-07-24  9:59   ` Claudio

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180724102506.42114a68@gandalf.local.home \
    --to=rostedt@goodmis.org \
    --cc=claudio.fontana@gliwa.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).