Re: [Iscsitarget-devel] Re: [ANNOUNCE] iSCSI enterprise target software

[Dmitry Yusupov <dmitry_yus@yahoo.com>]

On Wed, 2005-03-02 at 14:04 +0900, FUJITA Tomonori wrote:
> From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> Subject: [Iscsitarget-devel] Re: [ANNOUNCE] iSCSI enterprise target software
> Date: Tue, 01 Mar 2005 18:35:49 +0900
> 
> > The last reason is that user-space cost like memory copy. With 1Gbs
> > Ethernet, is is not critical. However, with 10G, it is critical, I
> > expect. I've been setting up 10G experimental infrastructure to
> > evaluate iSCSI performance.
> 
> If we try to build high-performance iSCSI target software on 10Gbs
> Ethernet, I think that we need to implement it in the kernel
> space, although this topic is still in the research stage.
> 
> IICR, Intel provides open-source iSCSI target software, which uses
> mmap() in the user space, as you suggested. However, they chose a
> different approach to implement iSCSI target software for 10Gbs. They
> modified the Linux kernel TCP stack to fully integrate iSCSI
> functionality with it. It is still not clear how to get the best
> performance out of 10GBs Ethernet, however, it seems that using just
> the socket interface is not good enough. So I think that we need to
> control all the system-resources to do it.
> 
> We've not optimized our code yet. The current code simply uses the
> socket interface, however, moving some functionality to the TCP stack
> can improve the performance, although I don't plan to modify theu TCP
> stack. A possible approach to do it is exploiting sk_data_ready().

www.open-iscsi.org project uses this technique on receiving path and
shows very nice performance numbers for Read operations comparable with
HW accelerators.

To add such a functionality to an existing project will probably require
total re-design.

Regards,
Dima