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

From: Michael Breuer
Date: Thu Jan 07 2010 - 02:56:02 EST


On 1/7/2010 2:47 AM, Jarek Poplawski wrote:
On Thu, Jan 07, 2010 at 02:20:22AM -0500, Michael Breuer wrote:
...
Reapplied a couple of earlier patches - still can't do jumbo frames, but
the rx errors are gone and speed has improved. Too early to assure that
it's stable.

Patches that seem to fix the rx drops (all from Stephen):
1) Patch change to tx_init
2) Patch to lock netif_device_detach
3) Patch to sky2_tx_complete to add netif_device_present test
Also in the mix: Jarek's alternative 2
BTW, the main difference between alt. 1 and 2 is error notification:
alternative 2 doesn't hide some (most) of drops, so, dependending on
app, there might be more and faster retransmits. (I don't know what
apps used by you (other than dhcp) can depend so much on this.)

Unless I misread the code, I think that in some cases e skb is actually freed if the cfq (among others perhaps) scheduler returns an error on enqueue (flow control perhaps). Thus with alternative 1, it is possible that the skb is acted upon after being freed - this would be consistent with the DMAR errors I saw.

With this set and mtu=1500 all seems good - decent if not stellar
throughput; no logged errors; no reported packet loss. As before, will
leave running and see if anything falls apart.
Good news!

Jarek P.
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