Re: [PATCH] af_packet: Don't use skb after dev_queue_xmit()

From: Michael Breuer
Date: Mon Jan 18 2010 - 16:26:14 EST

On 1/18/2010 4:00 PM, Stephen Hemminger wrote:
On Mon, 18 Jan 2010 15:56:45 -0500
Michael Breuer<mbreuer@xxxxxxxxxx> wrote:

2. The dropped tx packet (DHCP) is a bit harder to recreate, but it
still happens.

You might want to use tc filter rule to set priority of DHCP packets
higher. This would cause them to be in a separate queue and eliminate
the problem.

Ok - for fun, tried that - no change. Not sure I see why this might be a factor. The packet loss happens when TX load is low and RX high.
Also, packets only being dropped if traversing a router the router itself. Keep in mind that pings to the router did not lose packets, pings through the router lost packets. The router was not under load (traffic is being generated from a device connected via the 1Gb switch, not the wifi router), and tcpdump on the router input port shows the pings to the router, but not the ones through the router.

One added note, when I just tried this, the test data ended while the packet loss was occurring. The DHCPOFFER packet loss did not clear until about a minute after the throughput abated. I really think something is getting hosed, and I'd but some weird interaction with the arp logic high on the list of suspects. Not sure what else would be a factor when looking at the extra hop on the same subnet.
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