[ofa-general] QoS RFC / how its linked to the networking stack QoS?

[Or Gerlitz]

Sean Hefty wrote:
>> I wonder how you think the suggested scheme for IPoIB plugs into the 
>> existing QoS flow at the Linux network stack. Looking on the man pages 
>> of tcp(7) and ip(7) I see that there's a SOL_SOCKET level option of 
>> SO_PRIORITY and SOL_IP level option of IP_TOS.
> 
> I was looking at IB routing, not IP routing.  IPv6 uses flow info, 
> which, from what I can tell, is traffic class and flow label.

Indeed, that the IP_TOS option is related to IP routing and the 
SO_PRIORITY option might be more related to internal net stack QoS such 
as Priority Queuing, where both are beyond the scope of IPoIB.

However, As I reported below, for IPoEth the equivalent of IPoIB such as 
the 802.1q and e1000 drivers are using skb->priority to derive the 
"Ethernet QoS" which is the equivalent the SL in the LRH etc.

>> Looking lower in the stack, on the IPoEth scheme where the 802.1q is 
>> used for the VLAN header generation, the code seems to generate the 
>> p_bits field of the header using skb->priority (see the call to 
>> vlan_dev_get_egress_qos_mask() from vlan_dev_hard_header() at 
>> net/8021q/vlan_dev.c)
> 
> Someone with more knowledge of IPoIB than me needs to provide input 
> here.  I thought the use of different PKeys was similar to the selection 
> of a VLAN.

Yes, use of pkeys with IPoIB is a similar concept for use of VLANs with 
IPoEth, the point here, is that Ethernet QoS comes into play only when 
VLANs are used, since the standard MAC header does not specify any QoS.

For IPoIB (no GRH case, omitting IB transport header) you would have

< LRH | IPoIB header | IP header | etc >

and for IPoEth using 802.1q VLANs

< MAC header | 802.1q vlan tag | IP header | etc >

the vlan tag has 12 bits of "vlan id" (the equiv of pkey), 3 bits of 
priority (the equiv of the SL) and one more bit i don't remember.

Or.