RE: iSCSI: freeing resources during data-in and r2t

[Black_David@emc.com]

Eddy,

 

The A bit in Data-In plus Data ACK (SNACK type 2 in -14, Julian's

renumbering of the SNACK types in the working version of -15 is/will

be/has been undone) already provides the intermediate resource freeing

for Data-In.  This is only available for ErrorRecoveryLevel >= 1

We've never thought that R2Ts would consume enough resources to

be worth putting in support for intermediate resource

freeing of them.  Adding another sequence number at this late date

to deal with a "slight inefficiency" when the A bit is used properly

(SNACK-Data ACK PDUs vs. a piggybacked count) does not seem like a

good idea.

 

Thanks,

--David

-----Original Message-----
From: Eddy Quicksall [mailto:eddy_quicksall@ivivity.com]
Sent: Wednesday, July 17, 2002 12:15 PM
To: Mallikarjun C. (E-mail)
Cc: ips@ece. cmu. edu (E-mail)
Subject: RE: iSCSI: freeing resources during data-in and r2t

I think see a slight inefficiency in how resources are freed when multiple data-in and r2t's PDU's are used when ErrorRecoverLevel > 0 or TCP ACK is not available to the iSCSI layer.

 

Data-in and R2T's use DataSN and R2TSN. To free those resources, ExpStatSN is used.

 

But if several R2T's and/or Data-in PDU's were used, resources used for those PDU's are tied up for the entire command.

 

Since other commands could be received during this time, it would be nice if those commands could contain information that would tell the target that the R2T and/or Data-in PDU's have been received.

 

I know a radical change at this point is probably a bad idea but I just wanted to throw out the idea ... if the StatSN/ExpStatSN were changed to something like RespSN/ExpRespSN and if everything going from the target to the initiator carried a new RespSN, then the resources could be freed up sooner.

 

I would hate to use the A bit for this because it causes more traffic.

 

Eddy

mailto:Eddy_Quicksall@iVivity.com