Hello Herbert,
In commit "[NET]: Added GSO toggle"
37c3185a02d4b85fbe134bf5204535405dd2c957,
you force NETIF_F_HW_CSUM if GSO feature is selected.
By default, SW GSO is active as soon as a network board has NETIF_F_SG
feature.
This means that function sk_setup_caps() forces NETIF_F_HW_CSUM for any
board having NETIF_F_SG
For boards having no HW checksum capability, this results in performance
loss due to data copy being done in skb_do_copy_data_nocache() with
copy_from_user() then checksum being done later with csum_partial()
instead of getting both done at the same time using
csum_and_copy_from_user()
Is there a reason for forcing NETIF_F_HW_CSUM ?
Christophe
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