Hi, when using "fq_codel" as network scheduler, I noticed an issue with IEEE 802.15.4 6LoWPAN fragmentation. The issue is that high payloads IPv6 packets are dropped. I detected the issue on the sending side which segments the 6LoWPAN packet into several fragments. In the IEEE 802.15.4 6LoWPAN fragmentation we have a 6LoWPAN interface (MTU 1280) on top of an IEEE 802.15.4 interface (MTU 127). The 6LoWPAN fragmentation algorithm creates in the "ndo_start_xmit" netdev_ops callback function of the 6LoWPAN interface new sk_buffs for the underlaying IEEE 802.15.4 interface (as skb->dev) and sends them via a dev_queue_xmit. IEEE 802.15.4 is a very slow connection and after each transmit there is an "interframe spacing time" which depends on frequency setting. In my testcase, that's about ~500 us for a payload above 18 bytes. This is done by calling netif_stop_queue for the interface and start a timer after each transmitted frame according to the interframe spacing time. When the timer fires, it wakes the queue again by calling netif_wake_queue. Now: What I am noticed with fq_codel is that the code at [0] will drop high payloaded IPv6 packets. Of course, if we have an IPv6 packet of more than 1280 bytes payload we have a fragmentation (IPv6 fragmentation) over a fragmentation (802.15.4 6LoWPAN fragmentation). When I increase the "params->interval" parameter I can send a "longer" IPv6 packet depending how much I increase the "params->interval" parameter. I assume that the "params->interval" which defaults to MS2TIME(100) is too small. I further assume that at the beginning of fragmentation the interval measurement starts "vars->first_above_time = now + params->interval;" (line 247 at [0]) and while sending several fragments with the above mentioned interframe spacing time, the sending takes too long and the skb will be dropped. My questions are: - What's the best way to deal with something like that? - Is there a way to set the "params->interval" _per interface_? So I can change the default parameter to a suitable value in the "ndo_init" callback of the 6LoWPAN interface. Thanks in advance. - Alex [0] http://lxr.free-electrons.com/source/include/net/codel.h#L248 -- To unsubscribe from this list: send the line "unsubscribe linux-wpan" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
