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net/qdisc: IFF_NO_QUEUE drivers should use consistent TX queue len
The flag IFF_NO_QUEUE marks virtual device drivers that doesn't need a default qdisc attached, given they will be backed by physical device, that already have a qdisc attached for pushback. It is still supported to attach a qdisc to a IFF_NO_QUEUE device, as this can be useful for difference policy reasons (e.g. bandwidth limiting containers). For this to work, the tx_queue_len need to have a sane value, because some qdiscs inherit/copy the tx_queue_len (namely, pfifo, bfifo, gred, htb, plug and sfb). Commita813104d92
("IFF_NO_QUEUE: Fix for drivers not calling ether_setup()") caught situations where some drivers didn't initialize tx_queue_len. The problem with the commit was choosing 1 as the fallback value. A qdisc queue length of 1 causes more harm than good, because it creates hard to debug situations for userspace. It gives userspace a false sense of a working config after attaching a qdisc. As low volume traffic (that doesn't activate the qdisc policy) works, like ping, while traffic that e.g. needs shaping cannot reach the configured policy levels, given the queue length is too small. This patch change the value to DEFAULT_TX_QUEUE_LEN, given other IFF_NO_QUEUE devices (that call ether_setup()) also use this value. Fixes:a813104d92
("IFF_NO_QUEUE: Fix for drivers not calling ether_setup()") Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -7651,7 +7651,7 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
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if (!dev->tx_queue_len) {
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dev->priv_flags |= IFF_NO_QUEUE;
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dev->tx_queue_len = 1;
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dev->tx_queue_len = DEFAULT_TX_QUEUE_LEN;
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}
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dev->num_tx_queues = txqs;
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