Messages in this thread | | | Subject | Re: [PATCH] net: orphan queued skbs if device tx can stall | From | Eric Dumazet <> | Date | Tue, 10 Apr 2012 10:55:00 +0200 |
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On Tue, 2012-04-10 at 11:41 +0300, Michael S. Tsirkin wrote: > On Tue, Apr 10, 2012 at 09:55:58AM +0200, Eric Dumazet wrote:
> > In your case I would just not use qdisc at all, like other virtual > > devices. > > I think that if we do this, this also disables gso > for the device, doesn't it?
Not at all, thats unrelated.
> If true that would be a problem as this would > hurt performance of virtualized setups a lot.
In fact, removing qdisc layer will help a lot, removing a contention point.
Anyway, with a 500 packet limit in TUN queue itself, qdisc layer should be always empty. Whats the point storing more than 500 packets for a device ? Thats a latency killer.
> > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > > index bb8c72c..fd8c7f0 100644 > > --- a/drivers/net/tun.c > > +++ b/drivers/net/tun.c > > @@ -396,7 +396,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) > > sk_filter(tun->socket.sk, skb)) > > goto drop; > > > > - if (skb_queue_len(&tun->socket.sk->sk_receive_queue) >= dev->tx_queue_len) { > > + if (skb_queue_len(&tun->socket.sk->sk_receive_queue) >= TUN_READQ_SIZE) { > > if (!(tun->flags & TUN_ONE_QUEUE)) { > > /* Normal queueing mode. */ > > /* Packet scheduler handles dropping of further packets. */ > > tx_queue_len is controllable by SIOCSIFTXQLEN > so we'll need to override SIOCSIFTXQLEN somehow > to avoid breaking userspace that actually uses SIOCSIFTXQLEN, right?
Right now, you control with this tx_queue_len both the qdisc limit (if pfifo_fast default) and the receive_queue in TUN.
That doesnt seem right to me, and more a hack/side effect.
Maybe you want to introduce a new setting, only controling receive queue limit, and use tx_queue_len for its original meaning.
Then, setting tx_queue_len to 0 permits to remove qdisc layer, as any other netdevice.
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