Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C0BBC282E1 for ; Tue, 23 Apr 2019 12:41:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D80672175B for ; Tue, 23 Apr 2019 12:41:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727228AbfDWMlm (ORCPT ); Tue, 23 Apr 2019 08:41:42 -0400 Received: from s3.sipsolutions.net ([144.76.43.62]:32790 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726033AbfDWMll (ORCPT ); Tue, 23 Apr 2019 08:41:41 -0400 Received: by sipsolutions.net with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1hIujv-0007rP-1P; Tue, 23 Apr 2019 14:41:35 +0200 Message-ID: <99da695257304d32b65e2db8b7ada06759087c90.camel@sipsolutions.net> Subject: Re: [PATCH 5/5] mac80211: set NETIF_F_LLTX when using intermediate tx queues From: Johannes Berg To: Toke =?ISO-8859-1?Q?H=F8iland-J=F8rgensen?= , Herbert Xu Cc: Arend Van Spriel , Felix Fietkau , linux-wireless@vger.kernel.org, Eric Dumazet , netdev@vger.kernel.org Date: Tue, 23 Apr 2019 14:41:33 +0200 In-Reply-To: <87tvexrnxm.fsf@toke.dk> (sfid-20190417_112604_778209_602EB19C) References: <20190416074444.pdubbh6fbibdnhi7@gondor.apana.org.au> <73b18131-2777-da5c-a6ee-9d9b3e13cd06@broadcom.com> <20190416083636.5ttvezqyhzr2worg@gondor.apana.org.au> <87ef62uwfm.fsf@toke.dk> <95f86cf69dee05a176625925657cf0df0e97b5c9.camel@sipsolutions.net> <20190416093707.dtlwcmitzqopaeaw@gondor.apana.org.au> <20190416131346.u2uolljlrd5t2jro@gondor.apana.org.au> <87wojut7f7.fsf@toke.dk> <20190417033834.ep6t7r6ttvjek5g7@gondor.apana.org.au> <87tvexrnxm.fsf@toke.dk> (sfid-20190417_112604_778209_602EB19C) Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-2.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Wed, 2019-04-17 at 10:17 +0100, Toke Høiland-Jørgensen wrote: > Herbert Xu writes: > > > On Tue, Apr 16, 2019 at 02:18:36PM +0100, Toke Høiland-Jørgensen wrote: > > > > > > > The congestion control happens at two levels. You are right that the > > > > socket buffer acts as one limit. However, other applications may also > > > > rely on the TX queue being full as the throttle (by setting a > > > > sufficiently large socket buffer size). > > > > > > Do you happen to have an example of an application that does this that > > > could be used for testing? :) > > > > Have a look at > > > > commit 6ce9e7b5fe3195d1ae6e3a0753d4ddcac5cd699e > > Author: Eric Dumazet > > Date: Wed Sep 2 18:05:33 2009 -0700 > > > > ip: Report qdisc packet drops > > > > You should be able to do a UDP flood while setting IP_RECVERR to > > detect the packet drop due to a full queue which AFAICS will never > > happen with the current mac80211 setup. > > Also, looking at udp.c, it seems it uses net_xmit_errno() - which means > that returning NET_XMIT_CN has the same effect as NET_XMIT_SUCCESS when > propagated back to userspace? Which would kinda defeat the point of > going to the trouble of propagating up the return code (the mac80211 > queue will never drop the most recently enqueued packet)... I guess there might be value in returning NET_XMIT_CN anyway, but I think you're right in that we can never return anything but NET_XMIT_SUCCESS or NET_XMIT_CN since we never drop this new packet, just older ones. Which, btw, is exactly the same with net/sched/sch_fq_codel.c, AFAICT? johannes