** Changed in: linux (Ubuntu Trusty) Importance: Undecided => Medium ** Changed in: linux (Ubuntu) Importance: Undecided => Medium
** Changed in: linux (Ubuntu) Importance: Medium => High ** Changed in: linux (Ubuntu Trusty) Importance: Medium => High -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1344323 Title: Trusty kernel network performance regression Status in “linux” package in Ubuntu: Fix Released Status in “linux” source package in Trusty: In Progress Bug description: SRU Justification: Impact: Reduced TCP/IP receive performance for network devices that do not split packet headers into skb linear area (e.g., mlx4). The trusty kernel has incorporated commit eff44f9cc9a02aad53d568d3ae5020b6792ae4f6 Author: Jerry Chu <hk...@google.com> Date: Wed Dec 11 20:53:45 2013 -0800 net-gro: Prepare GRO stack for the upcoming tunneling support which modifies the GRO frag0 optimization, but unfortunately for some cases results in calls to __skb_pull_tail for every packet being received via the GRO path. This causes a reduction in TCP receive performance (or, more accurately, an increase in CPU load for TCP receive processing, which will cause throughput reduction for CPU limited workloads). Fix: This has already been fixed in mainline in commit a50e233c50dbc881abaa0e4070789064e8d12d70 Author: Eric Dumazet <eduma...@google.com> Date: Sat Mar 29 21:28:21 2014 -0700 net-gro: restore frag0 optimization The fix has been backported to and verified on the trusty kernel using mlx4 devices and iperf; an increase from 7.5 to 8.5 Gb/sec was observed when adding the patch, and the relevant portion of perf captures show changes in the call paths from: 7.17% iperf [kernel.kallsyms] [k] __pskb_pull_tail | --- __pskb_pull_tail | |--48.03%-- tcp_gro_receive | tcp4_gro_receive | inet_gro_receive | dev_gro_receive | napi_gro_frags | mlx4_en_process_rx_cq | mlx4_en_poll_rx_cq | net_rx_action | __do_softirq [...] |--28.53%-- napi_gro_frags | mlx4_en_process_rx_cq | mlx4_en_poll_rx_cq | net_rx_action | __do_softirq [...] |--13.11%-- inet_gro_receive | dev_gro_receive | napi_gro_frags | mlx4_en_process_rx_cq | mlx4_en_poll_rx_cq | net_rx_action | __do_softirq to: 4.87% iperf [kernel.kallsyms] [k] skb_gro_receive | --- skb_gro_receive | |--98.13%-- tcp_gro_receive | tcp4_gro_receive | inet_gro_receive | dev_gro_receive | napi_gro_frags | mlx4_en_process_rx_cq | mlx4_en_poll_rx_cq | net_rx_action | __do_softirq Testcase: The fix was tested using mlx4 10Gb/sec network devices between two arm64 systems using "iperf -s" on one end and "iperf -c" on the other. The unmodified kernel reported approximately 7.5 Gb/sec throughput, the fixed kernel approximately 8.5 Gb/sec. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1344323/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
