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Sat, 09 Nov 2019 03:22:50 -0800 (PST) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 960BE1800CC; Sat, 9 Nov 2019 12:22:49 +0100 (CET) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Kan Yan , Johannes Berg Cc: linux-wireless@vger.kernel.org, Make-Wifi-fast , ath10k@lists.infradead.org, John Crispin , Lorenzo Bianconi , Felix Fietkau , Rajkumar Manoharan , Kevin Hayes Subject: Re: [PATCH v6 3/4] mac80211: Implement Airtime-based Queue Limit (AQL) In-Reply-To: References: <157182473951.150713.7978051149956899705.stgit@toke.dk> <157182474287.150713.12867638269538730397.stgit@toke.dk> <1a2eb096119c9029e67caf797564d6511c8803a7.camel@sipsolutions.net> <87a796fxgd.fsf@toke.dk> <874kzefwt3.fsf@toke.dk> <300bf0146db6c0d5890699b3911d35174d28c9c0.camel@sipsolutions.net> X-Clacks-Overhead: GNU Terry Pratchett Date: Sat, 09 Nov 2019 12:22:49 +0100 Message-ID: <87k189qoom.fsf@toke.dk> MIME-Version: 1.0 X-MC-Unique: uh3wY1LMOHiipDOk3ifcQQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org Kan Yan writes: > It is most likely just insufficient locking. active_txq_lock is per > AC, can't protect local->aql_total_pending_airtime against racing > conditions: > void ieee80211_sta_update_pending_airtime(...) > { > spin_lock_bh(&local->active_txq_lock[ac]); > ... > local->aql_total_pending_airtime -=3D tx_airtime; > ... > spin_unlock_bh(&local->active_txq_lock[ac]); > } Ohh, right; didn't even realise those were not per-AC as well... > After changing it to atomic_t, no more aql_total_pending_airtime > underflow so far :). Using atomic operation should also help reduce > CPU overhead due to lock contention, as > ieee80211_sta_update_pending_airtime() is often called from the tx > completion routine triggered by interrupts, often in a different core > than where __ieee80211_schedule_txq() is running. > > I will post a new version a bit later if the test goes well. Awesome! :) -Toke