Ok, I have a virtual machine which has a residual kernel of 3.16.0-0.bpo.4 (Debian wheezy-backport's) available I confirmed the issue is replicatable on that machine too.

The testing methodology is using ab from 12 other remote servers (hopefully in order to prevent collisions) at a fairly low rate of 1r/s (the virtual machine with this older kernel is not particularly large). During this testing zero requests where received at one sampled process, while the first process showed approximately 10% CPU usage.

Regards,
Mathew



On Wed, Nov 25, 2015 at 12:42 AM, Valentin V. Bartenev <vbart@nginx.com> wrote:
On Wednesday 25 November 2015 00:25:19 SplitIce wrote:
> Hi all,
>
> I couldn't find anything in the mailing list about this issue, surely we
> are not the only one?
>
> When activating reuseport I am seeing all requests be served from a single
> nginx process. All others are just idling (SIGALARM interruption of
> epoll_wait / epoll_wait timeout according to strace).
>
> Process 442 attached - interrupt to quit
> epoll_wait(60, 8225010, 512, 4294967295) = -1 EINTR (Interrupted system
> call)
> --- SIGALRM (Alarm clock) @ 0 (0) ---
> rt_sigreturn(0xe)                       = -1 EINTR (Interrupted system call)
> epoll_wait(60, 8225010, 512, 4294967295) = -1 EINTR (Interrupted system
> call)
> --- SIGALRM (Alarm clock) @ 0 (0) ---
>
>
>
> This only occurs with reuseport, as soon as it is disabled the load is
> correctly distributed again.
>
> Configuration:
> worker_processes 12; # 2x8 cores on server
> multiple server blocks on different IP's and ports with reuseaddr.
> Linux kernel: 3.18.20
>
> Server nic has interrupts over all cores:
>
> # sudo ethtool -S eth0 |grep rx | grep pack
>      rx_packets: 11244443305
>      rx_queue_0_packets: 1381842455
>      rx_queue_1_packets: 1373383493
>      rx_queue_2_packets: 1490287703
>      rx_queue_3_packets: 1440591930
>      rx_queue_4_packets: 1378550073
>      rx_queue_5_packets: 1373473609
>      rx_queue_6_packets: 1437806438
>
>
> We have also experimented with disabling iptables and anything else on the
> server that could be interfering. I have also loaded it onto three other
> fresh servers with the same kernel (same OS image), but with different nic
> cards (with and without multiple rx queues) with no changes.
>
> This has me stumped. Ideas?
>

You should try another kernel.

  wbr, Valentin V. Bartenev

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