On Tue, Nov 5, 2024 at 11:07 AM <chia-yu.chang@xxxxxxxxxxxxxxxxxxx> wrote: > > From: Ilpo Järvinen <ij@xxxxxxxxxx> > > Handling the CWR flag differs between RFC 3168 ECN and AccECN. > With RFC 3168 ECN aware TSO (NETIF_F_TSO_ECN) CWR flag is cleared > starting from 2nd segment which is incompatible how AccECN handles > the CWR flag. Such super-segments are indicated by SKB_GSO_TCP_ECN. > With AccECN, CWR flag (or more accurately, the ACE field that also > includes ECE & AE flags) changes only when new packet(s) with CE > mark arrives so the flag should not be changed within a super-skb. > The new skb/feature flags are necessary to prevent such TSO engines > corrupting AccECN ACE counters by clearing the CWR flag (if the > CWR handling feature cannot be turned off). > > If NIC is completely unaware of RFC3168 ECN (doesn't support > NETIF_F_TSO_ECN) or its TSO engine can be set to not touch CWR flag > despite supporting also NETIF_F_TSO_ECN, TSO could be safely used > with AccECN on such NIC. This should be evaluated per NIC basis > (not done in this patch series for any NICs). > > For the cases, where TSO cannot keep its hands off the CWR flag, > a GSO fallback is provided by this patch. > > Signed-off-by: Ilpo Järvinen <ij@xxxxxxxxxx> > Signed-off-by: Chia-Yu Chang <chia-yu.chang@xxxxxxxxxxxxxxxxxxx> Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
