On Wed, 16 Nov 2016 16:34:09 -0800
Eric Dumazet <eric.duma...@gmail.com> wrote:
> On Wed, 2016-11-16 at 23:40 +0100, Jesper Dangaard Brouer wrote:
>
> > Using -R 1 does not seem to help remove __ip_select_ident()
> >
> > Samples: 56K of event 'cycles', Event count (approx.): 78628132661
> > Overhead Command Shared Object Symbol
> > + 9.11% netperf [kernel.vmlinux] [k] __ip_select_ident
> > + 6.98% netperf [kernel.vmlinux] [k] _raw_spin_lock
> > + 6.21% swapper [mlx5_core] [k] mlx5e_poll_tx_cq
> > + 5.03% netperf [kernel.vmlinux] [k]
> > copy_user_enhanced_fast_string
> > + 4.69% netperf [kernel.vmlinux] [k] __ip_make_skb
> > + 4.63% netperf [kernel.vmlinux] [k] skb_set_owner_w
> > + 4.15% swapper [kernel.vmlinux] [k] __slab_free
> > + 3.80% netperf [mlx5_core] [k] mlx5e_sq_xmit
> > + 2.00% swapper [kernel.vmlinux] [k] sock_wfree
> > + 1.94% netperf netperf [.] send_data
> > + 1.92% netperf netperf [.] send_omni_inner
>
> Check "ss -nu" ?
>
> You will see if sockets are connected (present in ss output or not)
Tested different versions of netperf, commands used below signature:
netperf-2.6.0: connected "broken"
netperf-2.7.0: connected works
SVN-r709 : connected works
I noticed there is a Send-Q, and the perf-top2 is _raw_spin_lock, which
looks like it comes from __dev_queue_xmit(), but we know from
experience that this stall is actually caused by writing the
tailptr/doorbell in the HW. Thus, this could benefit a lot from
bulk/xmit_more into the qdisc layer.
> UDP being connected does not prevent __ip_select_ident() being used.
>
> if ((iph->frag_off & htons(IP_DF)) && !skb->ignore_df) {
>
> So you need IP_DF being set, and skb->ignore_df being 0
Thanks for explaining that! :-)
http://lxr.free-electrons.com/source/include/net/ip.h?v=4.8#L332
http://lxr.free-electrons.com/source/net/ipv4/ip_output.c?v=4.8#L449
Netperf UDP_STREAM default send 64K packets that get fragmented...
which actually is very unfortunate because people end-up testing a code
path in the kernel they didn't expect. That is why I use the
option "-- -m 1472".
> time to try IP_MTU_DISCOVER ;)
To Rick, maybe you can find a good solution or option with Eric's hint,
to send appropriate sized UDP packets with Don't Fragment (DF).
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
Author of http://www.iptv-analyzer.org
LinkedIn: http://www.linkedin.com/in/brouer
Testing with ss -nua
$ /usr/local/stow/netperf-2.6.0-demo/bin/netperf -H 198.18.50.1 -t UDP_STREAM
-l 3 -- -m 1472 -n -N > /dev/null & sleep 1; ss -una
State Recv-Q Send-Q Local Address:Port Peer Address:Port
UNCONN 0 11520 *:54589 *:*
$ /usr/local/stow/netperf-2.7.0-demo/bin/netperf -H 198.18.50.1 -t UDP_STREAM
-l 3 -- -m 1472 -n -N > /dev/null & sleep 1; ss -una
State Recv-Q Send-Q Local Address:Port Peer Address:Port
ESTAB 0 18432 198.18.50.3:46803 198.18.50.1:51851
$ ~/tools/netperf2-svn/src/netperf -H 198.18.50.1 -t UDP_STREAM -l 3 -- -m 1472
-n -N > /dev/null & sleep 1; ss -una
State Recv-Q Send-Q Local Address:Port Peer Address:Port
ESTAB 0 43776 198.18.50.3:42965 198.18.50.1:51948
