[ofa-general] [PATCH RFC] rds: add iwarp support

[Olaf Kirch]

On Monday 07 July 2008 22:18:19 Steve Wise wrote:
> Sean Hefty wrote:
> >> The reason for not using rdma_resolve_addr() is to avoid having to
> >> allocate and free a cm_id each time we just want to find the local ib
> >> device, given a remote IP addr...
> >>     
> >
> > Can someone explain why this needed?  The local IB device is resolved as part of
> > the connection establishment process.  Why is an additional mechanism needed?
> >
> >   
> 
> RDS experts, correct me if this is wrong:

Essentially, you bind an RDS socket to an IP address, and that tells
RDS to pick a transport. That's what laddr_check is for - it's called
from bind() to determine what kind of transport to use.

Olaf

> 
> RDS exposes a reliable datagram service to user apps. To do this it 
> keeps connections to each host with RDS apps running and muxes user 
> datagrams over these connections using its own protocol. Further there 
> are 3 types of "transports" supported: TCP/IP, IB, and IW. When a user 
> app sends a datagram, the RDS module must figure out which transport 
> should be used. It does this based on the destination (and maybe local?) 
> ip addr of the RDS application's socket. Prior to the iWARP patch, the 
> way this transport switch decision was made was to look up the local 
> netdev based on the ipaddr(s) and if the netdev's ARP header type was 
> INFINIBAND, then obviously the IB transport should be used. With the 
> addition of iWARP, the decision is a little more complicated because the 
> iWARP netdev arp type is ETHERNET. So Jon added this new cma service to 
> find the netdev, then take the netdev mac address and search the gid 
> cache to see if that mac address was actually a gid for an rdma device. 
> If the mac addr was found, then we know this netdev supports rdma. 
> Creating the new service simply made this lookup light-weight by not 
> requiring a cm_id to be created, bound, etc.
> 
> Maybe there's a better way?
> 
> Steve.
> 
> 
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Olaf Kirch  |  --- o --- Nous sommes du soleil we love when we play
okir at lst.de |    / | \   sol.dhoop.naytheet.ah kin.ir.samse.qurax