Public bug reported:
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.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1344323
Title:
Trusty kernel network performance regression
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1344323/+subscriptions
--
ubuntu-bugs mailing list
ubuntu-bugs@lists.ubuntu.com
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
