svn commit: r189230 - head/sys/net

[Luigi Rizzo]

On Sun, Mar 01, 2009 at 12:42:54PM +0000, Robert Watson wrote:
> Author: rwatson
> Date: Sun Mar  1 12:42:54 2009
> New Revision: 189230
> URL: http://svn.freebsd.org/changeset/base/189230
> 
> Log:
>   Do a bit of struct ifnet cleanup in preparation for 8.0: group function
>   pointers together, move padding to the bottom of the structure, and add
>   two new integer spares due to attrition over time.  Remove unused spare
>   "flags" field, we can use one of the spare ints if we need it later.
>   
>   This change requires a rebuild of device driver modules that depend on
>   the layout of ifnet for binary compatibility reasons.

any chance to do similar things for other key kernel structures,
such as mbufs and struct bio ?

As an example, "struct bio" would benefit from at least one extra intptr_t
field to be used for classification purposes (see some recent work
we have been doing on disk scheduling). This is a rather trivial and
unintrusive change.

struct mbuf would benefit from a 'length' field, replacing the hardcoded
MLEN/MHLEN. This field would allow us to do several things, e.g.:

- use part of the data area to store m_tags instead of having
  to malloc() them separately;
- support multiple (or perhaps even runtime-configurable) mbuf sizes
  (and corresponding uma zones), so people could experiment with
  larger MBUFS and perhaps figure out what is the performance impact
  of using mbuf+clusters instead of individual mbufs for basically
  every incoming packet.

cheers
luigi