On Tue, 2012-12-11 at 13:34 -0500, David Miller wrote: > > You can't signal "out of descriptors" and stop the queue after the > fact. NETDEV_TX_BUSY is for handling exceptional and extraordinary > conditions, not for the normal queue full handling. This reminds me an idea I had about MQ/MQPRIO qdisc and BQL interaction (BQL btw makes less probable a NETDEV_TX_BUSY event or __QUEUE_STATE_DRV_XOFF state, but more probable a __QUEUE_STATE_STACK_XOFF) We dequeue a packet from qdisc, then we realize tx queue is in XOFF state, and we have to hold the skb into gso_skb for later. This shows in stats (tc -s qdisc dev eth0) as requeues. Problem of these requeues is that high priority packets can not be dequeued as long as this (possibly low prio and big TSO packet) is not removed from gso_skb. At 1Gbps speed, a full size TSO packet is 500 us of extra latency. Suggested fix : add a TCQ_F_MQSLAVE flag to allow dequeue_skb() to test the netif_xmit_frozen_or_stopped() status _before_ dequeing packet from qdisc. (For other qdiscs, we dont really know which tx queue will use the next packet before dequeueing it) -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
