On Tue, 2007-07-03 at 22:20 -0400, jamal wrote:

On Tue, 2007-03-07 at 14:24 -0700, David Miller wrote:
[.. some useful stuff here deleted ..]

quoted

That's why you have to copy into a purpose-built set of memory
that is composed of pages that _ONLY_ contain TX packet buffers
and nothing else.

The cost of going through the switch is too high, and the copies are
necessary, so concentrate on allowing me to map the guest ports to the
egress queues.  Anything else is a waste of discussion time, I've been
pouring over these issues endlessly for weeks, so if I'm saying doing
copies and avoiding the switch is necessary I do in fact mean it. :-)

ok, i get it Dave ;-> Thanks for your patience, that was useful.
Now that is clear for me, I will go back and look at your original email
and try to get back on track to what you really asked ;->

To expand on this, there are already "virtual" nic drivers in tree which
do the demux based on dst mac and send to appropriate other guest
(iseries_veth.c and Carsten Otte said the S/390 drivers do too).  lguest
and DaveM's LDOM make two more.

There is currently no good way to write such a driver.  If one recipient
is full, you have to drop the packet: if you netif_stop_queue, it means
a slow/buggy recipient blocks packets going to other recipients.  But
dropping packets makes networking suck.

Some hypervisors (eg. Xen) only have a virtual NIC which is
point-to-point: this sidesteps the issue, with the risk that you might
need a huge number of virtual NICs if you wanted arbitrary guests to
talk to each other (Xen doesn't support that, they route/bridge through
dom0).

Most hypervisors have a sensible maximum on the number of guests they
could talk to, so I'm not too unhappy with a static number of queues.
But the dstmac -> queue mapping changes in hypervisor-specific ways, so
it really needs to be managed by the driver...

Hope that adds something,
Rusty.