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[2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-485246ff886sm87283795e9.24.2026.03.09.04.44.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Mar 2026 04:44:11 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 0A86F5A1D3A; Mon, 09 Mar 2026 12:44:10 +0100 (CET) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Eric Dumazet , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , "David S . Miller" , Jakub Kicinski , Paolo Abeni Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, Simon Horman , Jamal Hadi Salim , Victor Nogueira , Cong Wang , Jiri Pirko , eric.dumazet@gmail.com, Eric Dumazet , Yunsheng Lin Subject: Re: [PATCH v2 net-next] net/sched: do not reset queues in graft operations In-Reply-To: <20260307163430.470644-1-edumazet@google.com> References: <20260307163430.470644-1-edumazet@google.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Mon, 09 Mar 2026 12:44:09 +0100 Message-ID: <87qzptp6ra.fsf@toke.dk> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Eric Dumazet writes: > Following typical script is extremely disruptive, > because each graft operation calls dev_deactivate() > which resets all the queues of the device. > > QPARAM=3D"limit 100000 flow_limit 1000 buckets 4096" > TXQS=3D64 > for ETH in eth1 > do > tc qd del dev $ETH root 2>/dev/null > tc qd add dev $ETH root handle 1: mq > for i in `seq 1 $TXQS` > do > slot=3D$( printf %x $(( i )) ) > tc qd add dev $ETH parent 1:$slot fq $QPARAM > done > done > > One can add "ip link set dev $ETH down/up" to reduce the disruption time: > > QPARAM=3D"limit 100000 flow_limit 1000 buckets 4096" > TXQS=3D64 > for ETH in eth1 > do > ip link set dev $ETH down > tc qd del dev $ETH root 2>/dev/null > tc qd add dev $ETH root handle 1: mq > for i in `seq 1 $TXQS` > do > slot=3D$( printf %x $(( i )) ) > tc qd add dev $ETH parent 1:$slot fq $QPARAM > done > ip link set dev $ETH up > done > > Or we can add a @reset_needed flag to dev_deactivate() and > dev_deactivate_many(). > > This flag is set to true at device dismantle or linkwatch_do_dev(), > and to false for graft operations. > > In the future, we might only stop one queue instead of the whole > device, ie call dev_deactivate_queue() instead of dev_deactivate(). > > I think the problem (quadratic behavior) was added in commit > 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and enqueue op > for lockless qdisc") but this does not look serious enough to deserve > risky backports. > > Signed-off-by: Eric Dumazet > Cc: Yunsheng Lin Reviewed-by: Toke H=C3=B8iland-J=C3=B8rgensen