[mvapich-discuss] mvapich2-0.9.8-branch question

[Kanoj Sarcar]

Hi Sundeep,

Ok, thanks, I see the rationale now. 

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

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

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?

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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> >
> 
> 



 
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