On 31 Mar 2005 16:10:32 -0500
Jamal Hadi Salim <hadi@xxxxxxxx> wrote:
> On Thu, 2005-03-31 at 15:04, Stephen Hemminger wrote:
> > 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
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