[net2-wg] tos msg vs ADU send for collection

[Omprakash Gnawali]

In terms of efficiency, tos msg send seems a clear winner of the two
approaches.

> I think the more important point is zero-copying policy that exposing
> TOS_Msg allows. As Phil pointed out, after you depart from the TOS_Msg
> for sending, you need to start copying data at least once.
> 
> It also has an implication on storage: if the application has the
> TOS_Msgs allocated and passes uses that for sending, then the stack
> doesn't need to allocate extra message buffers. On the other hand, if
> the application has the data in a buffer somewhere, this data needs to
> be copied to a message by the stack somewhere. Who has these buffers,
> and how many are they?
> 
> I would say it is slightly less convenient for application writers to
> have the TOS_Msgs instead of just worrying about data buffers, but
> there are some efficiency benefits.
> 
> I would say that some applications might be happy with just the
> TOS_Msg, and if needed be we could add a layer doing the packaging of
> data into packets as a higher level primitive. This packaging can even
> be shared with other forms of network protocol sending, and not only
> collection.
> 
> Thoughts?
> 
> Rodrigo
> 
> 
> On 1/13/06, Omprakash Gnawali <gnawali at usc.edu> wrote:
> >
> > This is a follow up on a specific thread from our meeting
> > yesterday. It was mentioned that providing tos msg send will enable
> > implementing ADU send on top of it but not necessarily the other way
> > around.
> >
> > It is not clear why this is the case. One can call the ADU send with a
> > tos msg as an argument; the ADU send which will package it inside its
> > own tos msg. The argument why this does not work is because there are
> > headers in a tos msg. As far as I can tell, collection applications do
> > not care about the header in a tos msg. Users of collection should
> > only care about data.
> >
> > Are there instances when users of collection care about the header ?
> > If there are instances of this then collection must provide a tos msg
> > send interface.
> >
> > - om_p
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