[Stgt-devel] uSpace Transport Patch

FUJITA Tomonori fujita.tomonori
Wed Aug 30 00:23:15 CEST 2006

From: Tom Tucker <tom at opengridcomputing.com>
Subject: Re: [Stgt-devel] uSpace Transport Patch
Date: Tue, 29 Aug 2006 09:47:59 -0500

> Tomo:
> At this point, I'm in thee middle of writing the kernel side of the  
> iSER transport. It would be no big deal to switch to user mode.  
> Should I do it?

I like to go with the user-space approach if it provides reasonable
performance. I cannot risk getting a refusal after a serious effort.
I don't like to duplicate open-iscsi kernel-space code in user-space,
however, it's much better than the future refusal.

The perfromance should be fine for iSER. For tcp, we would see small
drop, however, it should be fine. I've been working on the user-space
approach to see the performance. I replaced poll with epoll and added
AIO support. I'm making the out-of-date user-space code work with the
latest code. That sould be finished shortly.

I guess that I can merge the basic transport part of your latest

> We might want to look at the OpenFabric's stack to see how they  
> implement kernel bypass. This code has been accepted by kernel.org  
> and might provide a workable model or at least a starting point for  
> the user-mode iSER target implementation. It supports a very high  
> bandwidth, zero copy mechanism for exchanging data and events with  
> the kernel.

Sounds nice. I guess that you mean that user-space processes can
access to hardware without kernel intervention. Are documents about
the APIs available? I have some questions about event notifications,

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