netdev - Re: [PATCH net-next] net: stmmac: propagate feature flags to vlan

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Message-ID: <ZD2X8ALO3m7dmbOu@calimero.vinschen.de>
Date:   Mon, 17 Apr 2023 21:03:12 +0200
From:   Corinna Vinschen <vinschen@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        alexandre.torgue@...s.st.com, Jose Abreu <joabreu@...opsys.com>
Subject: Re: [PATCH net-next] net: stmmac: propagate feature flags to vlan

Hi Jakub,

On Apr 13 09:00, Jakub Kicinski wrote:
> On Thu, 13 Apr 2023 17:25:56 +0200 Corinna Vinschen wrote:
> > I tested that I can, for instance, set and reset the tx-checksumming
> > flag with ethtool -K.  As for TSO, I checked the source code, and the
> > function stmmac_tso_xmit handles VLANs just fine.  While different
> > NICs supported by stmmac have different offload features, there's no
> > indication in the driver source that VLANs have less offloading features
> > than a non-VLAN connection on the same HW.  Admittedly, I never saw
> > documentation explicitely claiming this.
> > 
> > If that's not sufficient, testing will take another day or two, because
> > I have to ask for a remote test setup first.
> 
> Testing would be great, I think it's worth waiting for that.

Yes, that was a good idea.  Turns out, TSO doesn't really work well
with VLANs.  The speed is... suboptimal.  Here are some results
with iperf, showing only the summary lines.

Base interface with TSO off:

$ ethtool -K enp0s29f1 tso off
$ iperf3 -c 192.168.1.2
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  1015 MBytes   852 Mbits/sec    0             sender
[  5]   0.00-10.04  sec  1012 MBytes   845 Mbits/sec                  receiver

Base interface with TSO on:

$ ethtool -K enp0s29f1 tso on
$ iperf3 -c 192.168.1.2
[...]
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  1.08 GBytes   928 Mbits/sec    0             sender
[  5]   0.00-10.04  sec  1.08 GBytes   921 Mbits/sec                  receiver

VLAN interface with TSO off:

$ ethtool -K enp0s29f1 tso off
$ iperf3 -c 192.168.3.2
[...]
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   975 MBytes   818 Mbits/sec    0             sender
[  5]   0.00-10.04  sec   973 MBytes   813 Mbits/sec                  receiver

VLAN interface with TSO on:

$ ethtool -K enp0s29f1 tso on
$ iperf3 -c 192.168.3.2
[...]
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  16.0 MBytes  13.4 Mbits/sec  899             sender
[  5]   0.00-10.04  sec  15.9 MBytes  13.3 Mbits/sec                  receiver

Oops.

I'll send a v2 patch which disables TSO on VLANs for the time being.


Corinna