From: "Michael S. Tsirkin" <[email protected]> Date: Mon, 3 Dec 2012 15:19:43 +0200
> Historically tun supported two modes of operation: > - in default mode, a small number of packets would get queued > at the device, the rest would be queued in qdisc > - in one queue mode, all packets would get queued at the device > > This might have made sense up to a point where we made the > queue depth for both modes the same and set it to > a huge value (500) so unless the consumer > is stuck the chance of losing packets is small. > > Thus in practice both modes behave the same, but the > default mode has some problems: > - if packets are never consumed, fragments are never orphaned > which cases a DOS for sender using zero copy transmit > - overrun errors are hard to diagnose: fifo error is incremented > only once so you can not distinguish between > userspace that is stuck and a transient failure, > tcpdump on the device does not show any traffic > > Userspace solves this simply by enabling IFF_ONE_QUEUE > but there seems to be little point in not doing the > right thing for everyone, by default. > > Signed-off-by: Michael S. Tsirkin <[email protected]> Now that TUN_NO_QUEUE has no real effect and is a NOP, please document it as such both in if_tun.h and the places in the driver that flip the bit based upon userspace requests. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
