From: Phil Sutter <p...@nwl.cc> Date: Thu, 13 Aug 2015 19:01:05 +0200
> This series adds a new private net_device flag indicating that a device may > (and probably should) be used without a queueing discipline attached to it. > This is already common practice for many virtual device types like e.g. > loopback, VLAN (802.1Q) or bridges (802.1D). The reason for this is that these > devices lack an underlying layer which could impose back pressure and > therefore > making a TX queue necessary to not slow down senders. > > Up to now, drivers being aware of the above applying to them set > dev->tx_queue_len to zero to indicate no qdisc should be attached to the > interface they drive and the kernel reacts upon this by assigning the noop > qdisc instead of the default pfifo_fast. This implicit agreement though leads > to an inconvenient situation once a user tries to attach a real qdisc to these > devices, as the formerly special tx_queue_len value becomes a regular one, > limiting the queue to zero packets and thus prevents any TX from happening. To > overcome this, practically all qdisc implementations intercept and sanitize > the > malicious value. > > With this series applied, drivers may signal the lack of need for a qdisc > without having to tamper with tx_queue_len, making fallbacks in qdiscs and > caveats in userspace unnecessary. > > Upon upstream acceptance, this series will be followed up by a set of patches > converting device drivers, adding a warning so out-of-tree driver authors get > aware of this change and dropping all special handling of tx_queue_len in > net/sched/. Series applied, thanks. Since the VRF changes went in right before this, I had to bump the IFF_NO_QUEUE value to use bit 26 instead of bit 25. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
