From: Greg Banks <gnb@sgi.com>
Subject: Re: [RFC,PATCH 11/15] knfsd: RDMA transport core
Date: Thu, 24 May 2007 02:35:58 +1000
Message-ID: <20070523163558.GQ14076@sgi.com>
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Cc: Tom Talpey <Thomas.Talpey@netapp.com>,
	Neil Brown <neilb@suse.de>, Peter Leckie <pleckie@melbourne.sgi.com>,
	Trond Myklebust <trond.myklebust@fys.uio.no>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Linux NFS Mailing List <nfs@lists.sourceforge.net>
To: Tom Tucker <tom@opengridcomputing.com>
In-Reply-To: <1179936164.9389.165.camel@trinity.ogc.int>
Sender: nfs-bounces@lists.sourceforge.net
Errors-To: nfs-bounces@lists.sourceforge.net

On Wed, May 23, 2007 at 11:02:44AM -0500, Tom Tucker wrote:
> On Wed, 2007-05-23 at 11:37 -0400, Trond Myklebust wrote:
> > On Wed, 2007-05-23 at 10:12 -0500, Tom Tucker wrote:
> > > Ah, this is a very good point. So then I think we need a transport
> > > specific deferral mechanism. 
> > 
> > No. I'm not sure that justifies a transport specific mechanism. It
> > rather calls for a more clever algorithm for deferring. Both NFSv3 and
> > NFSv4 have generic error messages that state 'I'm busy now, please try
> > again later'. As I said earlier, returning those errors are inevitably
> > more efficient than dropping.
> > Even for NFSv3 over TCP, dropping a single WRITE request will typically
> > cause a 60 second flat holdup instead of the more desirable retry +
> > exponential backoff.
> 
> Understood. My concern is very simple. I don't want to copy the data and
> to avoid this I need to have a way to save off the data for later
> processing in a transport specific way. All of my data is sitting in
> this rdma_context structure. 
> 
> The current svcsock approach just does a kmalloc and a memcpy. This is
> not a good approach for a 1MB NFS WRITE. 

Sure, but this is true regardless of the transport.

> An approach that allows a transport to give a "data cookie" to the
> deferral mechanism for later recovery would allow all the complexity to
> be centralized, but still allow the transport to keep the data around in
> it's own way.

I'm still confused.  Which data are you referring to?  Which
rdma_context structure, I don't see anything symbol like that in
the source?

Greg.
-- 
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
Apparently, I'm Bedevere.  Which MPHG character are you?
I don't speak for SGI.

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