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[37.136.75.139]) by smtp.gmail.com with ESMTPSA id r5-20020ac25a45000000b004f271790d6csm516383lfn.136.2023.06.03.08.44.45 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sat, 03 Jun 2023 08:44:46 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.100.0.2.22\)) From: Jonathan Morton In-Reply-To: Date: Sat, 3 Jun 2023 18:44:44 +0300 Cc: bloat@lists.bufferbloat.net Content-Transfer-Encoding: quoted-printable Message-Id: <39DED14A-AACF-4C45-9834-C295F92E8800@gmail.com> References: To: John D X-Mailer: Apple Mail (2.3654.100.0.2.22) Subject: Re: [Bloat] SQM tuning question X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 03 Jun 2023 15:44:48 -0000 > On 3 Jun, 2023, at 4:56 pm, John D via Bloat = wrote: >=20 > On the website it says the following: >=20 > CoDel is a novel =E2=80=9Cno knobs=E2=80=9D, =E2=80=9Cjust works=E2=80=9D= , =E2=80=9Chandles variable bandwidth and RTT=E2=80=9D, and simple AQM = algorithm. >=20 > =E2=80=A2 It is parameterless =E2=80=94 no knobs are required = for operators, users, or implementers to adjust. > =E2=80=A2 It treats good queue and bad queue differently - that = is, it keeps the delays low while permitting bursts of traffic. > =E2=80=A2 It controls delay, while insensitive to round-trip = delays, link rates, and traffic loads. > =E2=80=A2 It adapts to dynamically changing link rates with no = negative impact on utilization. >=20 > But everywhere I have read about about hardware which implements SQM = (including the bufferbloat website) it describes the need to tune based = on actual internet connection speed. > These seem to conflict especially that "handles variable bandwidth" = bit. Have I misunderstood or do the algorithms used in modern hardware = just not provide this part typically? My connection performance is quite = variable and I'm worried about crippling SQM to the lowest speed seen. SQM in practice requires three components: 1: Flow isolation, so that different flows don't affect each others' = latency and are delivered fairly; 2: Active Queue Management (AQM) to signal flows to slow down = transmissions when link capacity is exceeded; 3: Bandwidth shaping to match the queue to the available capacity. CoDel is, in itself, only the AQM component. It does indeed work pretty = well with no additional tuning - but only in combination with the other = two components, or when applied directly to the actual bottleneck. = Unfortunately in most consumer internet links, the actual bottleneck is = inaccessible for this purpose. Thus an artificial bottleneck must be = introduced, at which SQM is applied. The most convenient tool for applying all three SQM components at once = is Cake. This includes implementations of advanced flow isolation, = CoDel AQM, and a deficit-mode bandwidth shaper. All you really need to = do is to tell it how much bandwidth you have in each direction, minus a = small margin to ensure it becomes the actual bottleneck and can exert = the necessary control. When your available bandwidth varies over time, that can be = inconvenient. There are methods, however, of observing how available = capacity tends to change over time (typically on diurnal and weekly = patterns, if the variations are due to congestion in the ISP backhaul or = peering) and scheduling adjustments on that basis. If you have more = information on your situation, we might be able to give more detailed = advice. - Jonathan Morton=