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Subject: Re: [PATCH v3 3/6] mac80211: Add airtime accounting and scheduling to TXQs To: =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , Rajkumar Manoharan , linux-wireless@vger.kernel.org, ath10k@lists.infradead.org Cc: make-wifi-fast@lists.bufferbloat.net References: <1542063113-22438-1-git-send-email-rmanohar@codeaurora.org> <1542063113-22438-4-git-send-email-rmanohar@codeaurora.org> <871s7nv9pl.fsf@toke.dk> From: Felix Fietkau Openpgp: preference=signencrypt Autocrypt: addr=nbd@nbd.name; prefer-encrypt=mutual; keydata= xsDiBEah5CcRBADIY7pu4LIv3jBlyQ/2u87iIZGe6f0f8pyB4UjzfJNXhJb8JylYYRzIOSxh ExKsdLCnJqsG1PY1mqTtoG8sONpwsHr2oJ4itjcGHfn5NJSUGTbtbbxLro13tHkGFCoCr4Z5 Pv+XRgiANSpYlIigiMbOkide6wbggQK32tC20QxUIwCg4k6dtV/4kwEeiOUfErq00TVqIiEE AKcUi4taOuh/PQWx/Ujjl/P1LfJXqLKRPa8PwD4j2yjoc9l+7LptSxJThL9KSu6gtXQjcoR2 vCK0OeYJhgO4kYMI78h1TSaxmtImEAnjFPYJYVsxrhay92jisYc7z5R/76AaELfF6RCjjGeP wdalulG+erWju710Bif7E1yjYVWeA/9Wd1lsOmx6uwwYgNqoFtcAunDaMKi9xVQW18FsUusM TdRvTZLBpoUAy+MajAL+R73TwLq3LnKpIcCwftyQXK5pEDKq57OhxJVv1Q8XkA9Dn1SBOjNB l25vJDFAT9ntp9THeDD2fv15yk4EKpWhu4H00/YX8KkhFsrtUs69+vZQwc0cRmVsaXggRmll dGthdSA8bmJkQG5iZC5uYW1lPsJgBBMRAgAgBQJGoeQnAhsjBgsJCAcDAgQVAggDBBYCAwEC HgECF4AACgkQ130UHQKnbvXsvgCgjsAIIOsY7xZ8VcSm7NABpi91yTMAniMMmH7FRenEAYMa VrwYTIThkTlQzsFNBEah5FQQCACMIep/hTzgPZ9HbCTKm9xN4bZX0JjrqjFem1Nxf3MBM5vN CYGBn8F4sGIzPmLhl4xFeq3k5irVg/YvxSDbQN6NJv8o+tP6zsMeWX2JjtV0P4aDIN1pK2/w VxcicArw0VYdv2ZCarccFBgH2a6GjswqlCqVM3gNIMI8ikzenKcso8YErGGiKYeMEZLwHaxE Y7mTPuOTrWL8uWWRL5mVjhZEVvDez6em/OYvzBwbkhImrryF29e3Po2cfY2n7EKjjr3/141K DHBBdgXlPNfDwROnA5ugjjEBjwkwBQqPpDA7AYPvpHh5vLbZnVGu5CwG7NAsrb2isRmjYoqk wu++3117AAMFB/9S0Sj7qFFQcD4laADVsabTpNNpaV4wAgVTRHKV/kC9luItzwDnUcsZUPdQ f3MueRJ3jIHU0UmRBG3uQftqbZJj3ikhnfvyLmkCNe+/hXhPu9sGvXyi2D4vszICvc1KL4RD aLSrOsROx22eZ26KqcW4ny7+va2FnvjsZgI8h4sDmaLzKczVRIiLITiMpLFEU/VoSv0m1F4B FtRgoiyjFzigWG0MsTdAN6FJzGh4mWWGIlE7o5JraNhnTd+yTUIPtw3ym6l8P+gbvfoZida0 TspgwBWLnXQvP5EDvlZnNaKa/3oBes6z0QdaSOwZCRA3QSLHBwtgUsrT6RxRSweLrcabwkkE GBECAAkFAkah5FQCGwwACgkQ130UHQKnbvW2GgCfTKx80VvCR/PvsUlrvdOLsIgeRGAAn1ee RjMaxwtSdaCKMw3j33ZbsWS4 Message-ID: <8e7847ff-4c88-10ae-2223-2fc7321641d9@nbd.name> Date: Thu, 15 Nov 2018 12:09:08 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <871s7nv9pl.fsf@toke.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On 2018-11-14 18:40, Toke Høiland-Jørgensen wrote: >> This part doesn't really make much sense to me, but maybe I'm >> misunderstanding how the code works. >> Let's assume we have a driver like ath9k or mt76, which tries to keep a >> number of aggregates in the hardware queue, and the hardware queue is >> currently empty. >> If the current txq entry is kept at the head of the schedule list, >> wouldn't the code just pull from that one over and over again, until >> enough packets are transmitted by the hardware and their tx status >> processed? >> It seems to me that while fairness is still preserved in the long run, >> this could lead to rather bursty scheduling, which may not be >> particularly latency friendly. > > Yes, it'll be a bit more bursty when the hardware queue is completely > empty. However, when a TX completion comes back, that will adjust the > deficit of that sta and cause it to be rotated on the next dequeue. This > obviously relies on the fact that the lower-level hardware queue is > sufficiently shallow to not add a lot of latency. But we want that to be > the case anyway. In practice, it works quite well for ath9k, but not so > well for ath10k because it has a large buffer in firmware. > > If we requeue the TXQ at the end of the list, a station that is taking > up too much airtime will fail to be throttled properly, so the > queue-at-head is kinda needed to ensure fairness... Thanks for the explanation, that makes sense to me. I have an idea on how to mitigate the burstiness within the driver. I'll write it down in pseudocode, please let me know if you think that'll work. do { struct ieee80211_txq *pending_txq[4]; int n_pending_txq = 0; int i; if (hwq->pending < 4) break; nframes = 0; ieee80211_txq_schedule_start(hw, ac) do { bool requeue = false; struct ieee80211_txq *txq; txq = ieee80211_next_txq(hw, ac); if (!txq) break; nframes += schedule_txq(txq, &requeue); if (requeue) pending_txq[n_pending_txq++] = txq; } while (n_pending_txq < ARRAY_SIZE(pending_txq)); for (i = n_pending_txq; i > 0; i--) ieee80211_return_txq(hw, pending_txq[i - 1]); ieee80211_txq_schedule_end(hw, ac) } while (nframes); - Felix