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[34.48.33.21]) by smtp.gmail.com with UTF8SMTPSA id 71dfb90a1353d-54a88d5efbbsm1754249e0c.27.2025.09.22.05.52.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Sep 2025 05:52:32 -0700 (PDT) Date: Mon, 22 Sep 2025 08:52:32 -0400 From: Willem de Bruijn To: Eric Dumazet , "David S . Miller" , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , Willem de Bruijn , Kuniyuki Iwashima , netdev@vger.kernel.org, eric.dumazet@gmail.com, Eric Dumazet Message-ID: In-Reply-To: <20250922104240.2182559-1-edumazet@google.com> References: <20250922104240.2182559-1-edumazet@google.com> Subject: Re: [PATCH v4 net-next] udp: remove busylock and add per NUMA queues Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Eric Dumazet wrote: > busylock was protecting UDP sockets against packet floods, > but unfortunately was not protecting the host itself. > > Under stress, many cpus could spin while acquiring the busylock, > and NIC had to drop packets. Or packets would be dropped > in cpu backlog if RPS/RFS were in place. > > This patch replaces the busylock by intermediate > lockless queues. (One queue per NUMA node). > > This means that fewer number of cpus have to acquire > the UDP receive queue lock. > > Most of the cpus can either: > - immediately drop the packet. > - or queue it in their NUMA aware lockless queue. > > Then one of the cpu is chosen to process this lockless queue > in a batch. > > The batch only contains packets that were cooked on the same > NUMA node, thus with very limited latency impact. > > Tested: > > DDOS targeting a victim UDP socket, on a platform with 6 NUMA nodes > (Intel(R) Xeon(R) 6985P-C) > > Before: > > nstat -n ; sleep 1 ; nstat | grep Udp > Udp6InDatagrams 1004179 0.0 > Udp6InErrors 3117 0.0 > Udp6RcvbufErrors 3117 0.0 > > After: > nstat -n ; sleep 1 ; nstat | grep Udp > Udp6InDatagrams 1116633 0.0 > Udp6InErrors 14197275 0.0 > Udp6RcvbufErrors 14197275 0.0 > > We can see this host can now proces 14.2 M more packets per second > while under attack, and the victim socket can receive 11 % more > packets. > > I used a small bpftrace program measuring time (in us) spent in > __udp_enqueue_schedule_skb(). > > Before: > > @udp_enqueue_us[398]: > [0] 24901 |@@@ | > [1] 63512 |@@@@@@@@@ | > [2, 4) 344827 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| > [4, 8) 244673 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ | > [8, 16) 54022 |@@@@@@@@ | > [16, 32) 222134 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ | > [32, 64) 232042 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ | > [64, 128) 4219 | | > [128, 256) 188 | | > > After: > > @udp_enqueue_us[398]: > [0] 5608855 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| > [1] 1111277 |@@@@@@@@@@ | > [2, 4) 501439 |@@@@ | > [4, 8) 102921 | | > [8, 16) 29895 | | > [16, 32) 43500 | | > [32, 64) 31552 | | > [64, 128) 979 | | > [128, 256) 13 | | > > Note that the remaining bottleneck for this platform is in > udp_drops_inc() because we limited struct numa_drop_counters > to only two nodes so far. > > Signed-off-by: Eric Dumazet > Acked-by: Paolo Abeni Reviewed-by: Willem de Bruijn