linux-kernel - Re: [PATCH v10 0/2] Introducing trace buffer mapping by user-space

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Message-ID: <20240109082057.2bb6da70@gandalf.local.home>
Date: Tue, 9 Jan 2024 08:20:57 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Vincent Donnefort <vdonnefort@...gle.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
 kernel-team@...roid.com
Subject: Re: [PATCH v10 0/2] Introducing trace buffer mapping by user-space


Hi Masami, thanks for looking at this.

On Tue, 9 Jan 2024 22:04:45 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> > The tracing ring-buffers can be stored on disk or sent to network
> > without any copy via splice. However the later doesn't allow real time
> > processing of the traces. A solution is to give userspace direct access
> > to the ring-buffer pages via a mapping. An application can now become a
> > consumer of the ring-buffer, in a similar fashion to what trace_pipe
> > offers.  
> 
> I think this is very nice feature. But this series seems just a feature,
> no document and no example code. Can you add 2 patches to add those?
> I know libtracefs already provide a support code, but I think it is
> better to have a test code under tools/testing/selftests/ring_buffer.

Yeah, we should have sample code and a test.

> 
> I also wonder what happen if other operation (e.g. taking snapshot) happens
> while mmaping the ring buffer.

Hmm, good point. We should disable snapshots when mapped, and also prevent
mapping with latency tracer if we are not already doing that.

-- Steve