RE: checking immediate data

[John Hufferd <hufferd@us.ibm.com>]

Eddy,
I guess I do not put this trivial immediate data check in the same league as some of the other possible performance path checks.  I do not think that I can be convinced that checking a "flag" that says that I can or can't accept immediate data will impact the performance path.  And with that in mind, I support David's comments.
.
.
John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/System Group, San Jose CA
Main Office: (408) 256-0403, Tie: 276-0403, eFax: (408) 904-4688
Alt Office: (408) 997-6136, Cell: (408) 499-9702
Internet Address: hufferd@us.ibm.com

Eddy Quicksall <eddy_quicksall@ivivity.com> Sent by: owner-ips@ece.cmu.edu 08/08/2003 06:34 AM

To:        Black_David@emc.com, Julian_Satran@il.ibm.com         cc:        ips@ece.cmu.edu         Subject:        RE: checking immediate data

First, note that I realize it is too late to change this but I just want to
comment that using that rational, it would seem that the target should be
checking many other things that the initiator may do wrong. Obviously, that
would eventually effect performance; and this thinking is not consistent
with the consensus on another thread going on here regarding checking the
ITT for reuse.

In general, this kind of requirement should not appear in a performance
path.

Eddy

-----Original Message-----
From: Black_David@emc.com [mailto:Black_David@emc.com] 
Sent: Friday, August 08, 2003 9:26 AM
To: Julian_Satran@il.ibm.com; eddy_quicksall@ivivity.com
Cc: ips@ece.cmu.edu
Subject: RE: checking immediate data

Eddy and Julian

In the current specification, the target requirement also avoids
an interoperability problem if a broken initiator sends immediate
data that it has no business sending - since in the absence of the
requirement, target acceptance of the immediate data will be
implementation-dependent, the result is an annoying "sometimes
it works, sometimes it doesn't" situation.

It's better to have the initiator fail the first time it tries this
and get fixed, as opposed to building up an installed base where this
works when it shouldn't, as that would eventually cause removal of
the ImmediateData negotiation key, as targets would always have to
accept immediate data to deal with broken initiators who don't
know how not to send it.

Thanks,
--David
----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
black_david@emc.com        Mobile: +1 (978) 394-7754
----------------------------------------------------

> -----Original Message-----
> From: Julian Satran [mailto:Julian_Satran@il.ibm.com] 
> Sent: Friday, August 08, 2003 1:25 AM
> To: Eddy Quicksall
> Cc: Ips@Ece.Cmu.Edu (ips@ece.cmu.edu); owner-ips@ece.cmu.edu
> Subject: Re: checking immediate data
> 
> 
> The reason beyond this was that a 'highly optimized target may have 
> prepared already the R2T. I guess that you are objecting to 
> the second 
> MUST in the sentence  and I guess that except for recovery it 
> is a bit too 
> strong. For recovery however you might end up having a 
> different sequence 
> in recovery vs. original.
> 
> Regards,
> Julo
> 
> 
> 
> Eddy Quicksall <eddy_quicksall@ivivity.com> 
> Sent by: owner-ips@ece.cmu.edu
> 07/08/2003 19:34
> 
> To
> "Ips@Ece.Cmu.Edu (ips@ece.cmu.edu)" <ips@ece.cmu.edu>
> cc
> 
> Subject
> checking immediate data
> 
> 
> 
> 
> 
> 
> Section 12.11 says:
>  
> If ImmediateData is set to No and InitialR2T is set to Yes, then the
> initiator MUST NOT send unsolicited data and the target MUST reject
> unsolicited data with the corresponding response code.
>  
>  
> If the initiator says ImmediateData=No and the target has the 
> capability 
> of taking immediate data BUT the initiator sends immediate 
> data anyway, 
> why should the target be responsible to make that check (as 
> long as it 
> isn't going to break the target)? 
>  
> Eddy
>  
>