From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: netif_rx packet dumping Date: Thu, 3 Mar 2005 12:38:11 -0800 Message-ID: <20050303123811.4d934249@dxpl.pdx.osdl.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@oss.sgi.com To: Injong Rhee , John Heffner , "David S. Miller" , Yee-Ting Li , Baruch Even Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Both BIC TCP 1.1 and TCP-H include patches to disable the queue throttling behaviour of netif_rx. The existing throttling algorithm causes all packets to be dumped (until queue emptys) when the packet backlog reaches netdev_max_backog. I suppose this is some kind of DoS prevention mechanism. The problem is that this dumping action creates mulitple packet loss that forces TCP back to slow start. But, all this is really moot for the case of any reasonably high speed device because of NAPI. netif_rx is not even used for any device that uses NAPI. The NAPI code path uses net_receive_skb and the receive queue management is done by the receive scheduling (dev->quota) of the rx_scheduler. My question is why did BIC TCP and TCP-H turn off the throttling? Was it because they were/are using older 2.4 devices without NAPI.