From: Greg Banks <gnb@sgi.com>
Subject: Re: [RFC,PATCH 11/15] knfsd: RDMA transport core
Date: Thu, 24 May 2007 00:55:57 +1000
Message-ID: <20070523145557.GN14076@sgi.com>
References: <1179510352.23385.123.camel@trinity.ogc.int>
	<20070518192443.GD4843@fieldses.org>
	<1179516988.23385.171.camel@trinity.ogc.int>
	<20070523140901.GG14076@sgi.com>
	<1179931410.9389.144.camel@trinity.ogc.int>
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Cc: "J. Bruce Fields" <bfields@fieldses.org>,
	Neil Brown <neilb@suse.de>, Tom Talpey <Thomas.Talpey@netapp.com>,
	Linux NFS Mailing List <nfs@lists.sourceforge.net>,
	Peter Leckie <pleckie@melbourne.sgi.com>
To: Tom Tucker <tom@opengridcomputing.com>
In-Reply-To: <1179931410.9389.144.camel@trinity.ogc.int>
Sender: nfs-bounces@lists.sourceforge.net
Errors-To: nfs-bounces@lists.sourceforge.net

On Wed, May 23, 2007 at 09:43:30AM -0500, Tom Tucker wrote:
> 
> > Tom, just curious but in the November there was actually a difference
> > between the sockets and RDMA versions, the latter didn't have this
> > line:
> > 
> >         rqstp->rq_res.buflen = PAGE_SIZE;
> 
> I changed the defer logic quite a bit. In fact, I don't think it worked
> last November when you got the code originally. The latest code is at
> linux-nfs.org/~tomtucker/linux-nfs-2.6.git

Thanks.  I have a checkout from there as of several days ago but
I haven't ported all my patches to use it yet.

> > So perhaps a better approach would be to slightly tweak the existing
> > generic defer & revisit logic to allow a transport to specify how
> > many bytes of transport header need to be preserved.  Then the
> > transport-specific code needs very little code to support defer &
> > revisit, and doesn't duplicate multiple complex and subtle functions
> > which mess with svc_sock internals.
> 
> The svcsock defer logic only supports a simple RPC without a page list.
> The logic even has a comment that says "FIX ME". So I assumed that in
> the fullness of time, any RPC could be deferred. If this is in fact the
> case, then I believe it is better to have a separate method. If it is
> not the case, then the defer logic can be made generic.  

I'm not sure what you mean here.

Currently neither svc_defer() nor svc_rdma_defer() support calls longer
than just the head, meaning that WRITE RPCs (only) are dropped and
retried instead of deferred.  This doesn't seem to be too much of a
problem; deferral happens so infrequently anyway.

If for some reason the svc_defer() was to have the "FIXME" actually
implemented, WRITE RPCs would magically start to be deferred rather
than dropped, for the sockets case and presumably also for the
RDMA case.  Is this a problem?

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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