On Thu, 2007-07-26 at 00:15 -0700, David Miller wrote:
> The netpoll code has to take that anyways in order to call
> into ->hard_start_xmit() to send out the packet it has
> pending, I'm leveraging that as a synchronization mechanism
> in the drivers because the locking options are limited
> given that netpoll can try to do this in any context whatsoever.
>
> > There is a measurable difference in oprofile. When passing small
> > packets, there's a non-trivial difference in throughput.
>
> Then please help come up with an alternate scheme, because these
> NAPI changes fix real limitations and bugs in the current code
> and unless we fix netpoll too we can't move forward.
>
I'm not very familiar with netpoll, but I am guessing that we need to
prevent concurrent calls to the TX cleanup code. For maximum
flexibility, we should let ->poll_controller() handle the locking as the
driver knows what kind of locking is best.
If the driver wants a simple solution, it can do what you did in the
patch: wrap the tx cleanup code with netif_tx_lock() and
netif_tx_unlock().
If a NAPI driver wants to be more clever, it can do something such as
this in tg3's poll_controller:
if (netif_rx_schedule_prep(dev, &tp->napi)) {
tg3_tx(tp);
netif_poll_enable(tp->napi);
}
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