RE: [Xen-devel] continued problems with large send offload in windows

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> I'm still trying to figure out what is going wrong with large send
> support in windows. I thought I was doing all the right things but
> obviously something is going wrong...
> 
> Windows sends my driver a packet of length 4434 with an mss of 1460,
> comprising of the following sg items (pages):
> Page 0 - addr 19efc312, length 54
> Page 1 - addr 02776000, length 4096
> Page 2 - addr 02777000, length 284
> 
> I put this onto the tx ring as follows:
> Slot 0 - pfn 19efc, offset 312, length 4434,
>
NETTXF_extra_info|NETTXF_csum_blank|NETTXF_data_validated|NETTXF_more_da
> ta
> Slot 1 - extra info - mss = 1460
> Slot 2 - pfn 02776000, offset 0, length 4096, NETTXF_more_data
> Slot 3 - pfn 02777000, offset 0, length 284
> 
> A tcpdump on Dom0 receives this as the following:
> (connection setup stuff - MSS = 1460)
> Packet 0 - TCP Seq = 1, Length = 24
> Packet 1 - TCP Seq = 25, Length = 4380
> Packet 2 - TCP Seq = 1485, Length = 2920
> Packet 3 - TCP Seq = 2945, Length = 1460
> 
> Dom0 meanwhile is sending acks and getting them all wrong... obviously
> things have fallen to pieces badly somewhere.
> 

I think I've figured it out - when Windows gives me a packet to send,
one of the OOB data fields tells me the MSS for a large send offload
operation. After sending, I'm supposed to put the actual number of bytes
I sent back in that field and I wasn't doing it. So 'Packet 2' above was
actually another packet from Windows with the unsent (according to what
I told Windows) data, not Dom0 making something up because I'd given it
some wrong information...

James

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel