Re: [PATCH] An argument for allowing applications to manually send RMPP packets if desired

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Mon, Sep 12, 2011 at 10:15:08AM -0700, Roland Dreier wrote:
> > But is this really needed? Consider that these 3,000 replies only
> > differ in their destination addresses - the actual data is
> > identical in all of them.  Moreover, the data returned for a query
> > like this changes only rarely in a production fabric - which means
> > that the response could be generated once and then and then
> > re-used to provide responses to multiple clients.
> >
> > To allow this, however, the SM must be allowed to explicitly
> > manage its own RMPP transmissions instead of sending each response
> > as a complete unit. If this is allowed, then the kernel no longer
> > needs to allocate large amounts of buffer space, and the SM can
> > build the results of certain queries in advance, updating them
> > only when the fabric changes, instead of recreating them each time
> > it receives an IB_MAD_METHOD_GET_TABLE.
> 
> It seems at least the SM side could be handled using writev() to
> splice together the data it wants to send.

How does that help avoid the kernel memory allocations?

I think having the option for RMPP in user space is a good idea, it
allows much more efficiency on the SM side..

Jason
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