[mvapich-discuss] mvapich2-0.9.8-branch question

[Sundeep Narravula]

Kanoj,

> Yes, the rnic I am working with can be put into a mode
> to guarantee in-order placement.

This is good for RDMA_FAST_PATH.

> I think a specifiable environment variable should be
> able to handle this case correctly, no?

We will be providing an option to enable RDMA_FAST_PATH with a specifiable
environment variable. This will be in the SVN in the next 1-2 days.

> In general, are there any online documents describing
> internals of mvapich/iwarp and the various settable
> parameters etc? For example, if a newbie wanted to
> understand the iwarp primitives used in a benchmark
> program (say one of the osu_benchmarks), how would he
> go about that?

All the information regarding the adjustable parameters of MVAPICH2 are
available from the MVAPICH2 user-guide.

http://nowlab.cse.ohio-state.edu/projects/mpi-iba/user_guide.html
http://nowlab.cse.ohio-state.edu/projects/mpi-iba/download-mvapich2/mvapich2_user_guide.html

Cheers,
  --Sundeep.

>
> Thanks.
>
> Kanoj
>
> --- Sundeep Narravula <narravul at cse.ohio-state.edu>
> wrote:
>
> > Hi Kanoj,
> >
> >   The RDMA_FAST_PATH that we use in mvapich2
> > involves polling on the last
> > byte of an expected message to flag message
> > completions on the remote
> > side. Since this is not guaranteed by iWARP we have
> > disabled this
> > by default for the iWARP mode.
> >
> > Does the RNIC you use guarantee inorder placement of
> > RDMA bytes into the
> > remote buffer? or guarantee that the last byte will
> > be placed last into
> > the user buffer?
> >
> > Regards,
> >   --Sundeep.
> >
> >
> > On Wed, 14 Feb 2007, Kanoj Sarcar wrote:
> >
> > > Hello all,
> > >
> > > I am a mpi/mvapich newbie looking at iwarp support
> > in
> > > mvapich2.
> > >
> > > Between 0.9.8 release and branch, in procedure
> > > rdma_get_control_parameters() in file
> > >
> >
> src/mpid/osu_ch3/channels/mrail/src/gen2/ibv_param.c,
> > > I see a difference that I am trying to understand.
> > >
> > > In the release version, the code was:
> > >
> > >    if ((value =
> > getenv("MV2_DISABLE_RDMA_FAST_PATH"))
> > > != NULL) {
> > >         proc->has_adaptive_fast_path = 0;
> > >         rdma_polling_set_limit       = 0;
> > >     } else {
> > >         proc->has_adaptive_fast_path = 1;
> > >     }
> > >
> > > but this got changed in the branch version to also
> > > turn off adaptive fast path in case of iwarp.
> > >
> > > I am curious about the rationale for this change.
> > Is
> > > this to mostly support amasso card that (AFAIK)
> > does
> > > not have user mode fastpath support? Or is there
> > some
> > > architectural issue in current mvapich2 that
> > requires
> > > turning off fastpath on iwarp rnics?
> > >
> > > Thanks.
> > >
> > > Kanoj
> > >
> > > PS: please cc me on responses, I am not subscribed
> > to
> > > the list
> > >
> > >
> > >
> > >
> >
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