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

[Steven Rostedt]

Hi Masami, thanks for looking at this.

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