Re: [RFC PATCH] LTTng relay buffer allocation, read, write

Mathieu Desnoyers
2008-09-30T18:35:42Z

* Steven Rostedt (rostedt@goodmis.org) wrote:
>
> On Tue, 30 Sep 2008, Mathieu Desnoyers wrote:
> >
> > In Steven's scheme, the event IDs in the 4 bytes are reserved for
> > (useless) internal use ;) They can therefore not be used for specific
> > tracer event IDs, which I think is a misuse of the precious bits
> > otherwise available to store really useful event IDs.
>
> I'm using them, so they must not be totally useless. ;-)
>
> But ftrace has its own event ids and I don't want the ring buffer to ever
> have to know about them.
>
> -- Steve
>

You are actually using them to put redundant information that could be
encoded differently and thus save 4 bits per event records, more or less
what will be needed by most tracers (15 IDs, 1 reserved for an extended
ID field).

So the fact that you use them does not mean they are really required,
and I don't think such duplicated information actually makes things more
solid. Maybe just more obscure ?

Mathieu

--
Mathieu Desnoyers
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