Messages in this thread | | | Subject | Re: [PATCH] net: orphan queued skbs if device tx can stall | From | Eric Dumazet <> | Date | Tue, 10 Apr 2012 13:45:00 +0200 |
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On Tue, 2012-04-10 at 14:25 +0300, Michael S. Tsirkin wrote: > On Tue, Apr 10, 2012 at 12:04:19PM +0200, Eric Dumazet wrote: > > On Tue, 2012-04-10 at 12:31 +0300, Michael S. Tsirkin wrote: > > > > > True. Still this is the only interface we have for controlling > > > the internal queue length so it seems safe to assume someone > > > is using it for this purpose. > > > > > > > So to workaround a problem in tun, you want to hack net/core/dev.c :( > > Sorry about being unclear, I'm just saying that your patch assumes > tx_queue_len == 0 since you set it that way at device init but we can't > rely on this as existing users might have changed that value. > One way to fix would be a patch at the bottom: then we > can leave tun to treat tx_queue_len like it always did.
> ---- > > We don't want a queue for tun since it can stall forever, but userspace > might tweak it's tx_queue_len as a way to control RX queue depth, > and we don't want to break userspace. Use a private flag to disable queue. > > Warning: untested. > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c > index 27883d1..644ca53 100644 > --- a/net/sched/sch_generic.c > +++ b/net/sched/sch_generic.c > @@ -695,7 +692,7 @@ static void attach_one_default_qdisc(struct net_device *dev, > { > struct Qdisc *qdisc = &noqueue_qdisc; > > - if (dev->tx_queue_len) { > + if (dev->tx_queue_len && !(dev->priv_flags & IFF_TX_CAN_STALL)) { > qdisc = qdisc_create_dflt(dev_queue, > &pfifo_fast_ops, TC_H_ROOT); > if (!qdisc) {
Thing is this function is called before userspace can tweak tx_queue_len
So if you create a vlan device (this sets tx_queue_len to 0), no qdisc is attached.
If later userspace changes tx_queue_len to this device, qdisc wont automatically be created/attached.
Really, tx_queue_len is private to net/sched layer, it should not be used by tun device to control a receive queue limit.
Please try to not hack net/sched or net/core for your needs.
Its not because tun abused tx_queue_len in the past we must keep this hack forever.
In ethernet drivers, TX ring size is controlled by ethtool -g
Why tun driver would use another way ?
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