Re: [RFC,PATCH 11/15] knfsd: RDMA transport core

[Tom Tucker <tom@opengridcomputing.com>]

On Thu, 2007-05-24 at 00:55 +1000, Greg Banks wrote:
> 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?
> 

That's what I'm asking. I don't think it is, and if not, then I concur
we can normalize the defer logic.


> Greg.


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