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

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

* 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
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68