Re: iSCSI: SCSI Iniitator port: a simple approach, acceptable?

[Santosh Rao <santoshr@cup.hp.com>]

Somesh,

I don't understand your concern voiced below. 

A session spanning multiple adapters requires the host resident session
manager to co-ordinate assignment of initiator task tag, cmdsn,
exp_cmdsn & max_cmdsn, [over and beyond the usual initiator name &
ISID/TSID].

The initiator task tag & cmdsn can be passed down from the session
manager to the HBA in a mailbox command, as a part of issuing a new
iscsi command, and the (exp_cmdsn, max_cmdsn) values can be updated to
the host resident session manager by the HBA as a part of conveying a
mailbox command completion. There are no extra host interrupts in normal
I/O paths due to the presence of a host resident session manager.

If you're referring to locking overheads, then, these can be optimized
out.

I don't see why a host resident session manager affects performance of a
multi-connection session ? 

Regards,
Santosh

 

Somesh Gupta wrote:
> 
> Jim,
> 
> Multiple connections, especially when spread across multiple
> adapters will give performance that will be much less than
> that of multiple sessions in parallel (of course when there
> are multiple connections/session over multiple adapters - the
> adapters have to be able to take the session id from the
> host software - I obviously don't get the point of the debate).
> 
> There is no way a common synchronization point for
> command sequencing and flow control at the host level will not
> cause sub-standard performance. I have argued this point
> many times before, only to have it be brushed aside. Of course,
> only time will tell.
> 
> Somesh
> 


-- 
##################################
Santosh Rao
Software Design Engineer,
HP-UX iSCSI Driver Team,
Hewlett Packard, Cupertino.
email : santoshr@cup.hp.com
Phone : 408-447-3751
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