kernel-packages team mailing list archive

[Brad Figg <brad.figg@xxxxxxxxxxxxx>]

This bug is missing log files that will aid in diagnosing the problem.
>From a terminal window please run:

apport-collect 1344323

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable
to run this command, please add a comment stating that fact and change
the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the
Ubuntu Kernel Team.

** Changed in: linux (Ubuntu)
       Status: New => Incomplete

** Tags added: trusty

-- 
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:
  Incomplete

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 <hkchu@xxxxxxxxxx>
  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 <edumazet@xxxxxxxxxx>
  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