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

Mathieu Desnoyers
2008-09-30T18:14:52Z

* Martin Bligh (mbligh@google.com) wrote:
> On Tue, Sep 30, 2008 at 10:22 AM, Martin Bligh <mbligh@google.com> wrote:
> >> A 4 byte dataless payload is useless anyway.
> >
> > Not at all convinced that's true - we used it for lots of things.
> > Start and end of irq event is one frequent example.
> >
> > Also, in a compact mode, we can record start and end of
> > syscalls like this (without parameters).
>
> Ah, sorry, maybe I misread this. No data with no event ids, etc
> is fairly useless. 4 bytes data including space to record event ids is OK.

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.

Mathieu

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