Subject: linux-3.14-rc1 & PACKET_QDISC_BYPASS : slow_path warning

From: Mathias Kretschmer <[email-masked]>
Date: Mon, 3 Feb 2014 23:47:51 +0100

Hi Daniel,

we are developing a wired/wireless MPLS switch. Currently the data plane 
runs in user space using PF_PACKET sockets via RX_RING/TX_RING.

We had hoped to test the PACKET_QDISC_BYPASS option since this seems to 
be the proper optimization for our purposes.

Unfortunately, we're seeing a 'slow path' warning for every packet that 
is being sent out. With PACKET_QDISC_BYPASS disabled, no warnings are 
dumped. Hardware is an older AMD Geode LX embedded board (ALiX).

BTW, this happens while sending via a wireless (802.11) adhoc interface. 
Hence, it might be an interaction with the ieee80211 sub system.

Please, let me know if you need any further information.

Cheers,

Mathias

-- 
Dr. Mathias Kretschmer, Head of Competence Center
Fraunhofer FOKUS Network Research
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