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Date:   Mon, 17 Apr 2023 12:11:46 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Corinna Vinschen <vinschen@redhat.com>
Cc:     netdev@vger.kernel.org,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        alexandre.torgue@foss.st.com, Jose Abreu <joabreu@synopsys.com>
Subject: Re: [PATCH net-next] net: stmmac: propagate feature flags to vlan
Message-ID: <20230417121146.654b980d@kernel.org>
In-Reply-To: <ZD2X8ALO3m7dmbOu@calimero.vinschen.de>
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On Mon, 17 Apr 2023 21:03:12 +0200 Corinna Vinschen wrote:
> 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.

Hah, good to find out before users did :)

IIRC there is something in the TCP stack which retries sending 
as non-TSO if TSO keeps failing so "TSO is very slow" may in fact 
mean TSO is completely broken but TCP is managing to deliver a little
bit with just retransmissions or super tiny cwnd or some such.