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Date: Tue, 04 Feb 2014 13:56:01 +0100 From: Daniel Borkmann <dborkman@...hat.com> To: Mathias Kretschmer <mathias.kretschmer@...us.fraunhofer.de> CC: netdev@...r.kernel.org, "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>, Felix Fietkau <nbd@...nwrt.org>, Jesper Dangaard Brouer <jbrouer@...hat.com> Subject: Re: linux-3.14-rc1 & PACKET_QDISC_BYPASS : slow_path warning Hi Mathias, [cc'ing Felix] On 02/03/2014 11:47 PM, Mathias Kretschmer wrote: > 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. Hm, so the WARN_ON() is triggered inside ath9k driver in relation to 802.11 QoS, and came in from commit 066dae93bdf ("ath9k: rework tx queue selection and fix queue stopping/waking"). We did the stress testing of that option for PF_PACKET on 10Gbit/s NICs. Seems to me you might be running into the same issue when using pktgen as it randomly or per round-robin selects tx queues as well? Not entirely sure how necessary this WARN_ON() is though, Felix? I think QDISC_BYPASS might not be the best option in your case, perhaps you will run into increased power usage in your NIC as a side-effect? Cheers, Daniel -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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