RE: MPA alignment

Eddy,

I agree with your statement about software RDMA being a bit silly, but
only when the thought is about implementations on servers.

There is at least one type of environment where using RDMA with a
software iWARP stack may not be too silly, and that is when the object
of the interconnect is to optimize the over all costs and save Server
Cycles.  In that case is may make sense to operate with a software RDMA
stack on the desktop systems or workstations.  Those environments often
have a plentiful amount of available CPU cycles on the
desktop/workstation.  So, the approach is to burn CPU cycles at the
desktop/workstation and save CPU cycles on the servers, which have
RNICs.  This type of a configuration actually seems to be a useful
configuration.

 

The same argument can be used with iSCSI and iSER, but only in the case
where there are RNICs in the target.  It is a little bit strange, as you
point out, to have the storage controller implement a software version
of iSER, except perhaps for some type of compatibility or migration
reasons.

 

.

.

.

John L Hufferd

Sr. Executive Director of Technology

Brocade Communications Systems, Inc

[email protected]

Office Phone: (408) 333-5244; eFAX: (408) 904-4688

Alt Office Phone: (408) 997-6136; Cell: (408) 627-9606

 

  _____  

From: Eddy Quicksall [mailto:[email protected]] 
Sent: Tuesday, April 18, 2006 5:48 AM
To: Mike Ko
Cc: [email protected]
Subject: Re: [Ips] MPA alignment

 

Thanks,

 

Here is my feeling on this. If one were to use a standard TCP/IP stack
(that does copying) then it is a bit silly to use iSER. If one were to
use a software implementation and write/modify the stack to get the
desired effects of DDP then he will probably heed to the alignment notes
in the spec. So if one were to support misaligned segments using a
slower method then it would be OK.

 

Eddy

	----- Original Message ----- 

	From: Mike Ko <mailto:[email protected]>  

	To: Eddy Quicksall
<mailto:[email protected]>  

	Cc: [email protected] 

	Sent: Tuesday, April 18, 2006 2:16 AM

	Subject: Re: [Ips] MPA alignment

	 

	
	Eddy, 
	
	If your question is about MPA behavior in general, then it
should be directed to the rddp forum. 
	
	Assuming your question is related to iSER, then if iWARP is
implemented in software and uses the existing TCP/IP stack, then it
cannot guarantee that FPDU's will be aligned with TCP segments.  For the
general case where iWARP is implemented in an RNIC with an integrated
TCP/IP stack, then it is to the RNIC vendor's advantage to optimize his
product's performance and therefore FPDU's should be aligned with TCP
segments.  However, the receiver can still receive FPDU's which are not
aligned with TCP segments if there are resegmenting middleboxes
somewhere in the connection path. 
	
	Mike   

	To:        <[email protected]> 
	cc:         
	Subject:        [Ips] MPA alignment 
	
	
	It is preferable to have TCP sender to align MPA header where a
TCP segment begins and to keep the MPA FPDU within a TCP segment, so
that the receiver hardware doesn't need to temporarily buffer the FPDU
for the CRC checking.   
	  
	Does anyone know of any software or hardware that is not an FPDU
alignment sender? 
	Does anyone have a feel for the likelihood of software or
hardware to not align FPDU's on a TCP segment? 
	  
	Eddy_______________________________________________
	Ips mailing list
	[email protected]
	https://www1.ietf.org/mailman/listinfo/ips

	
  _____  


	_______________________________________________
	Ips mailing list
	[email protected]
	https://www1.ietf.org/mailman/listinfo/ips

_______________________________________________
Ips mailing list
[email protected]
https://www1.ietf.org/mailman/listinfo/ips