[lttng-dev] Sub-buffer multiplicity on multi-core systems

[Mathieu Desnoyers]

----- Original Message -----
> From: "Daniel Thibault" <Daniel.Thibault at drdc-rddc.gc.ca>
> To: lttng-dev at lists.lttng.org
> Sent: Thursday, October 10, 2013 8:33:56 AM
> Subject: Re: [lttng-dev] Sub-buffer multiplicity on multi-core systems
> 
> Date: Tue, 8 Oct 2013 17:57:23 -0400
> From: J?r?mie Galarneau <jeremie.galarneau at efficios.com>
> 
> > In kernel tracing, ring buffers are separate per CPU, per channel.
> > Each ring buffer is flushed into its own CTF data stream file. These
> > streams are only "merged" by Babeltrace (or any other reader) while
> > reading the trace.
> >
> > J?r?mie
> 
>    Thanks for confirming the 1:1 correspondence between channels and files.
>    I wanted to make sure I understood the ins and outs properly.

Not quite,

It's a 1:1 correspondence between ring buffer and file.

1:N correspondence between channel and ring buffers. (typically, N being the number of cpus)
(therefore 1:N correspondence between channel and files)

1:M correspondence between ring buffer and sub-buffers. (M being the number of subbuffers per buffers, configurable on a per-channel basis)
1:1 correspondence between sub-buffer and CTF trace packet.

Thanks,

Mathieu

> 
> Daniel U. Thibault
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-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com