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[146.241.44.112]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38058bb433bsm12391884f8f.112.2024.10.29.05.56.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 29 Oct 2024 05:56:24 -0700 (PDT) Message-ID: Date: Tue, 29 Oct 2024 13:56:22 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 net-next 1/1] sched: Add dualpi2 qdisc To: chia-yu.chang@nokia-bell-labs.com, netdev@vger.kernel.org, davem@davemloft.net, stephen@networkplumber.org, jhs@mojatatu.com, edumazet@google.com, kuba@kernel.org, dsahern@kernel.org, ij@kernel.org, ncardwell@google.com, koen.de_schepper@nokia-bell-labs.com, g.white@CableLabs.com, ingemar.s.johansson@ericsson.com, mirja.kuehlewind@ericsson.com, cheshire@apple.com, rs.ietf@gmx.at, Jason_Livingood@comcast.com, vidhi_goel@apple.com Cc: Olga Albisser , Olivier Tilmans , Henrik Steen , Bob Briscoe References: <20241021221248.60378-1-chia-yu.chang@nokia-bell-labs.com> <20241021221248.60378-2-chia-yu.chang@nokia-bell-labs.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20241021221248.60378-2-chia-yu.chang@nokia-bell-labs.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/22/24 00:12, chia-yu.chang@nokia-bell-labs.com wrote: > +/* Default alpha/beta values give a 10dB stability margin with max_rtt=100ms. */ > +static void dualpi2_reset_default(struct dualpi2_sched_data *q) > +{ > + q->sch->limit = 10000; /* Max 125ms at 1Gbps */ > + > + q->pi2.target = 15 * NSEC_PER_MSEC; > + q->pi2.tupdate = 16 * NSEC_PER_MSEC; > + q->pi2.alpha = dualpi2_scale_alpha_beta(41); /* ~0.16 Hz * 256 */ > + q->pi2.beta = dualpi2_scale_alpha_beta(819); /* ~3.20 Hz * 256 */ > + > + q->step.thresh = 1 * NSEC_PER_MSEC; > + q->step.in_packets = false; > + > + dualpi2_calculate_c_protection(q->sch, q, 10); /* wc=10%, wl=90% */ > + > + q->ecn_mask = INET_ECN_ECT_1; > + q->coupling_factor = 2; /* window fairness for equal RTTs */ > + q->drop_overload = true; /* Preserve latency by dropping */ > + q->drop_early = false; /* PI2 drops on dequeue */ > + q->split_gso = true; This is a very unexpected default. Splitting GSO packets earlier WRT the H/W constaints definitely impact performances in a bad way. Under which condition this is expected to give better results? It should be at least documented clearly. Thanks, Paolo