From: Eric Dumazet <redacted>
Date: Fri, 02 Jan 2015 10:24:00 -0800

On Thu, 2015-01-01 at 00:42 +1100, Herbert Xu wrote:

quoted

Firstly not many people test non-TSO code paths anymore so bugs
are likely to persist for a long time there.  Perhaps it's time
to remove the non-TSO code path altogether? The GSO code path
should provide enough speed-up in terms of boosting the effective
MTU to offset the cost of copying.

quoted

Secondly why are we dealing with hardware TSO segment limits
by limiting the size of the TSO packet in the TCP stack? Surely
in this case GSO is free since there won't be any copying?

It might depends on the device capabilities.

Non TSO/GSO path is known to be better for devices unable to perform TX
checksumming, as we compute the checksum at the time we copy data from
user to kernel (csum_and_copy_from_user() from tcp_sendmsg())).

Non-SG capable devices suffer in this scenerio as well.