Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932869AbcDNPop (ORCPT ); Thu, 14 Apr 2016 11:44:45 -0400 Received: from mail-pa0-f51.google.com ([209.85.220.51]:33822 "EHLO mail-pa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932214AbcDNPon (ORCPT ); Thu, 14 Apr 2016 11:44:43 -0400 Message-ID: <1460648680.10638.47.camel@edumazet-glaptop3.roam.corp.google.com> Subject: Re: Deleting child qdisc doesn't reset parent to default qdisc? From: Eric Dumazet To: Jiri Kosina Cc: Phil Sutter , Jamal Hadi Salim , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 14 Apr 2016 08:44:40 -0700 In-Reply-To: References: <1460646099.10638.44.camel@edumazet-glaptop3.roam.corp.google.com> <20160414151813.GE3715@orbyte.nwl.cc> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 968 Lines: 29 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())