Hello all, I am working on upstreaming a network driver for a Socionext SoC, and I am having some trouble figuring out why my TX performance is horrible when booting a Debian Stretch rootfs, while booting a Ubuntu 17.04 rootfs works absolutely fine. Note that this is using the exact same kernel image, booted off the network.
Under Ubuntu, I get the following iperf results from the box to my AMD Seattle based devbox with a 1 Gbit switch in between. (The NIC in question is also 1 Gbit) $ sudo iperf -c dogfood.local -r ------------------------------------------------------------ Server listening on TCP port 5001 TCP window size: 85.3 KByte (default) ------------------------------------------------------------ ------------------------------------------------------------ Client connecting to dogfood.local, TCP port 5001 TCP window size: 748 KByte (default) ------------------------------------------------------------ [ 5] local 192.168.1.112 port 51666 connected with 192.168.1.106 port 5001 [ ID] Interval Transfer Bandwidth [ 5] 0.0-10.0 sec 1.07 GBytes 920 Mbits/sec [ 4] local 192.168.1.112 port 5001 connected with 192.168.1.106 port 33048 [ 4] 0.0-10.0 sec 1.10 GBytes 940 Mbits/sec Booting the *exact* same kernel into a Debian based rootfs results in the following numbers $ sudo iperf -c dogfood.local -r ------------------------------------------------------------ Server listening on TCP port 5001 TCP window size: 85.3 KByte (default) ------------------------------------------------------------ ------------------------------------------------------------ Client connecting to dogfood.local, TCP port 5001 TCP window size: 85.0 KByte (default) ------------------------------------------------------------ [ 5] local 192.168.1.112 port 40132 connected with 192.168.1.106 port 5001 [ ID] Interval Transfer Bandwidth [ 5] 0.0-10.1 sec 4.12 MBytes 3.43 Mbits/sec [ 4] local 192.168.1.112 port 5001 connected with 192.168.1.106 port 33068 [ 4] 0.0-10.0 sec 1.10 GBytes 939 Mbits/sec The ifconfig stats look perfectly fine to me (TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0). During the TX test, the CPUs are almost completely idle. (This system has 24 cores, but not particularly powerful ones.) This test is based on v4.14-rc4, but v4.13 gives the same results. Could anyone please shed a light on this? What tuning parameters and/or stats should I be looking at? I am a seasoned kernel developer but a newbie when it comes to networking, so hopefully I just need a nudge to go looking in the right place. Thanks, Ard.
