[openib-general] FMR and how they work

[Caitlin Bestler]

On 5/4/05, Fab Tillier <ftillier at infiniconsys.com> wrote:
> > From: Dan Bar Dov [mailto:danb at voltaire.com]
> > Sent: Wednesday, May 04, 2005 1:00 AM
> >
> > Voltair's IB based ISER indeed uses kDAPL so it will be very simple to
> > atapt it to iWARP.
> > .
> > Voltaire's kDAPL supports FMR using PLATFORM registration type, and it is
> > used by the ISER implementation.
> >
> 
> Why doesn't iSER just use a single un-translated MR for all of physical
> memory (like the other kernel ULPs)?  It would then just call the DMA
> mapping functions and be done with it - no registration at all is going to
> be faster than FMRs.
> 


An FMR can be used to advertise a target buffer that is being read into
as a single logical buffer. Using physical memory would require

a) exporting the physical page list of where your buffers were (making
    the buffer advertisement larger and more complex)

b) Trusting whoever is on the other end of the connection with access
    to your entire physical memory.