From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.toke.dk (mail.toke.dk [IPv6:2a0c:4d80:42:2001::664]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id AA3DE3B29E for ; Tue, 6 Oct 2020 07:47:50 -0400 (EDT) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=toke.dk; s=20161023; t=1601984868; bh=6xgrwCAmmdAntS5xCQh4JEMhIcrV4fCbYBRqlhOZEM8=; h=From:To:Subject:In-Reply-To:References:Date:From; b=PYpLTErZVmkwWY73eTgrN6L0bOBs/ZWgDMhyPvNzrnIZHCQpTwXIBlYeyu1Qgzy3K jufkhAaNVhAOMj8A0aGBpPWgI5vXaHDYYkzC03kwLHV+DPDP+KRDlNy2RZB69WAYZc iH+UfSTOjAHDqea+IskulmFAi22nTO89UdaEiGgwhaxJSgl1Ma2vcKcjE+NFOE/ygx L4WOrAHsb4XPZi/6vjTjg1IK9NCBXgvlI3pS+e0Pft4F7Qu/+WrjQ114YVVmDAKyWs sRbyFE+HAaF2GA3EemOISRnQNzR+8GoJoZc7ZQNTgNc6Yr6NjXUkCpURL+sZ2FfXpQ U9iq5Y3Lxijqg== To: Michael Welzl , make-wifi-fast@lists.bufferbloat.net In-Reply-To: References: Date: Tue, 06 Oct 2020 13:47:47 +0200 X-Clacks-Overhead: GNU Terry Pratchett Message-ID: <87d01vfue4.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain 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 11:47:50 -0000 Michael Welzl writes: > Hi all, > > 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? > > Is it: > 1. the access point's downlink queue, feeding into the WiFi network, This we mostly fixed, but only if you're on a recent OpenWrt with the right WiFi drivers. Otherwise, this is a major source of latency *if* the WiFi link is faster than the downlink from the internet. 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. > 2. the modem's downlink queue, feeding into the access point, If your internet (downlink) connection is slower than your WiFi link, this is where you'll get the queueing. > 3. the modem's uplink queue, As above, but in the other direction - but as uplinks tend to be asymmetric, this direction is often more of a problem. > 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) 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). > or is it a combination of these? 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. > 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? It certainly used to be; but as uplink connection speeds improve, the bottleneck moves to the WiFi link. 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?). -Toke