On 31 Mar 2005 16:10:32 -0500
Jamal Hadi Salim [off-list ref] wrote:

On Thu, 2005-03-31 at 15:04, Stephen Hemminger wrote:

quoted

Here is another alternative that seems better than the earlier posting. It uses
a per device receive queue for non-NAPI devices.  The only issue is that then
we lose the per-cpu queue's and that could impact the loopback device performance.
If that is really an issue, then the per-cpu magic should be moved to the loopback
device.

The repurcassions of going from per-CPU-for-all-devices queue
(introduced by softnet) to per-device-for-all-CPUs maybe huge in my
opinion especially in SMP. A closer view of whats there now maybe
per-device-per-CPU backlog queue.

Any real hardware only has a single receive packet source (the interrupt routine),
and the only collision would be in the case of interrupt migration.  So having
per-device-per-CPU queue's would be overkill and more complex because
the NAPI scheduling is per-netdevice rather than per-queue (though that
could be fixed).

I think performance will be impacted in all devices. imo, whatever needs
to go in needs to have some experimental data to back it

Experiment with what? Proving an absolute negative is impossible.
I will test loopback and non-NAPI version of a couple of gigabit drivers
to see.