From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-out01.uio.no (mail-out01.uio.no [IPv6:2001:700:100:10::50]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id ABBF33B29E for ; Tue, 6 Oct 2020 08:15:35 -0400 (EDT) Received: from mail-mx10.uio.no ([129.240.10.27]) by mail-out01.uio.no with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93.0.4) (envelope-from ) id 1kPlsT-0006oA-38; Tue, 06 Oct 2020 14:15:33 +0200 Received: from boomerang.ifi.uio.no ([129.240.68.135]) by mail-mx10.uio.no with esmtpsa (TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256) user michawe (Exim 4.93.0.4) (envelope-from ) id 1kPlsS-000ABi-8b; Tue, 06 Oct 2020 14:15:33 +0200 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) From: Michael Welzl In-Reply-To: <87d01vfue4.fsf@toke.dk> Date: Tue, 6 Oct 2020 14:15:30 +0200 Cc: make-wifi-fast@lists.bufferbloat.net Content-Transfer-Encoding: quoted-printable Message-Id: References: <87d01vfue4.fsf@toke.dk> To: =?utf-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= X-Mailer: Apple Mail (2.3445.9.1) X-UiO-SPF-Received: Received-SPF: neutral (mail-mx10.uio.no: 129.240.68.135 is neither permitted nor denied by domain of ifi.uio.no) client-ip=129.240.68.135; envelope-from=michawe@ifi.uio.no; helo=boomerang.ifi.uio.no; X-UiO-Spam-info: not spam, SpamAssassin (score=-5.0, required=5.0, autolearn=disabled, AWL=0.009, UIO_MAIL_IS_INTERNAL=-5, uiobl=NO, uiouri=NO) X-UiO-Scanned: 2B401B1998620CF26E8DA7BB095230E5F6F89B4A Subject: Re: [Make-wifi-fast] Where is the bloat in WiFi? X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 06 Oct 2020 12:15:35 -0000 Hi, and thanks for a quick answer! But, it's not quite what I was looking for.... see below: > On 6 Oct 2020, at 13:47, Toke H=C3=B8iland-J=C3=B8rgensen = wrote: >=20 > Michael Welzl writes: >=20 >> Hi all, >>=20 >> A simple question to y'all who spent so much time on Cake and things >> ... in a household using WiFi, which buffer is usually bloated? Where >> does the latency really come from? >>=20 >> Is it: >> 1. the access point's downlink queue, feeding into the WiFi network, >=20 > This we mostly fixed, but only if you're on a recent OpenWrt with the > right WiFi drivers. Well okay... I was curious about where the bottleneck is. I can = translate my question into: "if Cake is installed everywhere, where does = it have the most work to do?". > Otherwise, this is a major source of latency *if* > the WiFi link is faster than the downlink from the internet. Huh? Slower, you mean? > This > depends on both the internet connection and the current rate each WiFi > station operates at, so it can vary wildly, and on very short time > scales. Sure... I was asking for the "if" in your statement above - since this = is an operationally-oriented list: what do people see? What is the more = common case? >> 2. the modem's downlink queue, feeding into the access point, >=20 > If your internet (downlink) connection is slower than your WiFi link, > this is where you'll get the queueing. Yes sure :-) see above: I wanted to know what the more common case = is, in households that people on this list have dealt with. >> 3. the modem's uplink queue, >=20 > As above, but in the other direction - but as uplinks tend to be > asymmetric, this direction is often more of a problem. >=20 >> 4. the access point's uplink queue towards the modem (hm, that = seems >> silly, surely the AP-modem connection is fast... so perhaps, instead: >> the queue in the host, as it wants to send data towards the access >> point) >=20 > Yeah, that would be in the host; but host drivers can suffer from = severe > bufferbloat as well, especially as rates drop (since the buffers are > often tuned for the maximum throughput the device can deliver in > best-case signal conditions). >=20 >> or is it a combination of these? >=20 > Usually it's a combination; especially since the WiFi capacity varies > wildly with signal conditions (as devices move around relative to the > AP), general link usage (more devices active mean less available > capacity for each device, exacerbated by airtime unfairness), and > interference. Also there are things like excessive retries causing HoL > blocking. Man, what an academic answer! Makes me think you have a PhD, or = something! What *theoretically* can happen is not what I was fishing = for :-D >> I guess that, with openwrt, Cake is operating on the queue that's >> feeding the wifi network, as the modem's queue is out of its >> control... so: is this where the bottleneck usually is? >=20 > It certainly used to be; but as uplink connection speeds improve, the > bottleneck moves to the WiFi link. Yessss, that's why I was asking.... > The extent to which this happens > depends on where you are in the world; personally I've been = bottlenecked > on the WiFi link ever since I got a fibre upstream (and with 802.11ax > rates maxing at >1Gbps, maybe that'll change again?). THIS is what I was after :) one data point, cool - so far, so = good... Cheers, Michael