Re: [PATCH] acenic - don't spin in hard_start_xmit when ring fills

[Stephen Hemminger <shemminger@xxxxxxxx>]

On Thu, 16 Sep 2004 16:22:50 -0700
"David S. Miller" <davem@xxxxxxxxxxxxx> wrote:

> On Thu, 16 Sep 2004 16:17:53 -0700
> Stephen Hemminger <shemminger@xxxxxxxx> wrote:
> 
> > Running performance tests on the acenic, I noticed that the driver
> > spins when the transmit ring gets full.  This might have been okay when
> > CPU's were slower, but it isn't the right thing to do. Better to
> > return TX_BUSY and let network scheduling handle it.
> 
> Acenic does completely lockless processing, are you sure you didn't
> add a race or bug?

NO, the bus just isn't fast enough to keep up with the number of small
packets I am shoving at it.

You got TX_LOCKED and TX_BUSY confused. The problem is drivers that
don't check to see if the last packet sent fills the ring and stop
themselves.

>       o NETDEV_TX_BUSY Cannot transmit packet, try later 
>         Usually a bug, means queue start/stop flow control is broken in
>         the driver. Note: the driver must NOT put the skb in its DMA ring.