Re: Deleting child qdisc doesn't reset parent to default qdisc?

[Eric Dumazet]

On Thu, 2016-04-14 at 17:34 +0200, Jiri Kosina wrote:
> On Thu, 14 Apr 2016, Phil Sutter wrote:
> 
> > OTOH some qdiscs (CBQ, DRR, DSMARK, HFSC, HTB, QFQ) assign the default
> > one upon deletion instead of noop_qdisc, hence I would describe
> > the situation using the words 'inconsistent' and 'accident' rather than
> > 'expected'. :)
> 
> Exactly. I'd again like to stress the fact that this configuration works:
> 
> 	jikos:~ # tc qdisc show
> 	qdisc tbf 10: dev eth0 root refcnt 2 rate 800Mbit burst 131000b lat 1.0ms 
> 
> and this (after performing add/delete operation) doesn't:
> 
> 	jikos:~ # tc qdisc show
> 	qdisc tbf 10: dev eth0 root refcnt 2 rate 800Mbit burst 131000b lat 1.0ms 
> 
> It's hard to spot a difference (hint: there is none).

This is because some qdisc are not visible in the dump.


qdisc_list_add() uses a single list, so adding too much stuff in it
could slow down fast path (qdisc_lookup(), called from
qdisc_tree_reduce_backlog())