PERFORCE change 129544 for review

[Kip Macy]

On Nov 26, 2007 3:55 AM, Robert Watson <rwatson at freebsd.org> wrote:
>
> On Mon, 26 Nov 2007, Kip Macy wrote:
>
> > http://perforce.freebsd.org/chv.cgi?CH=129544
> >
> > Change 129544 by kmacy at kmacy:storage:toestack on 2007/11/26 05:26:43
> >
> >       disable merging of data into existing mbufs if
> >       new SB_TOE flag is set
>
> One of the reasons we compact socket buffers with TCP and other stream
> protocols is that if you're dealing with an application/protocol that spits
> out data in small chunks (i.e., a series of printfs) and nagel is disabled,
> you end up with a series of packets that make quite inefficient use of mbufs,
> as the space wasted per chunk of data is significant.  Not only that, we bill
> for space in socket buffers based on the space held by the full mbuf, not just
> the data in the mbuf when it comes to socket buffer resource limits, so you
> can rapidly fill up socket buffer limits without compaction in this type of
> scenario.  I'm not sure which protocols this would affect, but I'd imagine
> that RPC-like protocols supporting asynchronous operation (so that you get a
> series of replies and responses in flight at once) might be relevant, such as
> IMAP.
>
> On an unrelated not, if we want a non-coalescing modes for socket bufferss, we
> should probably also give it a name like "SB_NOCOALESCE" rather than something
> TOE-specific.
>

I agree that making it toe specific is somewhat misleading. I actually
think I'll be able to fix my code so that it can cope with data being
added to the end of a cluster or mbuf that has already been
transmitted. If so, I won't need to pull this along when I bring TOE
support into CVS.

Thanks for the feedback.

 -Kip