Re: ISCSI: flow control

[Michael Krause <krause@cup.hp.com>]

At 10:53 AM 9/24/00 -0700, Pierre Labat wrote:


>T10 could add an advertising of a command credit. For example
>when the status is returned the target gives a command credit.

In essence, this is what InfiniBand does and others have been 
advocating.  When the ACK (SCSI response) is returned it encodes a credit 
to inform the sender of how many receives buffers (available command queue 
slots) have been posted. This allows the sender to know whether it can 
continue to issue send operations.  The cost is trivial in hardware and 
greatly simplifies the software / control logic since it can post as many 
commands as it wants on the requester and these will be processed at the 
rate the receiver can actually consume them.  When combined with the RNR 
NAK operation (still applicable since there may be other reasons for 
returning this), one can achieve a fairly robust and simple implementation 
that works across a wide range of products.

Mike