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Subject: Re: [OMPI devel] [OMPI svn-full] svn:open-mpi r29055 - in trunk/ompi/mca: btl btl/smcuda common/cuda pml/ob1
From: George Bosilca (bosilca_at_[hidden])
Date: 2013-08-23 07:36:14


On Aug 22, 2013, at 19:24 , Rolf vandeVaart <rvandevaart_at_[hidden]> wrote:

> Hi George:
> The reason it tainted the PML is because the CUDA IPC support makes use of the large message RDMA protocol of the PML layer. The smcuda btl starts up, but does not initially support any large message RDMA (RGET,RPUT) protocols. Then when a GPU buffer is first accessed, the smcuda btl starts an exchange of some control messages with its peer. If they determine that they can support CUDA IPC, then the smcuda calls up into the PML layer and says it is OK to start using the large message RDMA. This all happens in code that is only compiled in if the user asks for CUDA-aware support.

The issue is not that is compiled in only when CUDA support is enabled. The problem is that it is a breakage of the separation between PML and BTL. Almost all BTL did manage to implement highly optimized protocols under this design without having to taint the PML. Very similarly to CUDA I can cite CMA and KNEM support in the SM BTL. So I really wonder why the CUDA support is so different, at the point where it had to go all over the place (convertor, memory pool and PML)?

> The key requirement was I wanted to dynamically add the support for CUDA IPC when the user first started accessing GPU buffers rather than during MPI_Init.

Moving from BTL flags to endpoint based flags is indeed a good thing. This is something that should be done everywhere in the PML code, as it will allow the BTL to support different behaviors based on the peer.


> This the best way I could figure out how to accomplish this but I am open to other ideas.

> Thanks,
> Rolf
>> -----Original Message-----
>> From: devel [mailto:devel-bounces_at_[hidden]] On Behalf Of George
>> Bosilca
>> Sent: Thursday, August 22, 2013 11:32 AM
>> To: devel_at_[hidden]
>> Subject: Re: [OMPI devel] [OMPI svn-full] svn:open-mpi r29055 - in
>> trunk/ompi/mca: btl btl/smcuda common/cuda pml/ob1
>> I'm not very keen of seeing BTL modification tainting the PML. I would have
>> expected support for IPC between GPU must be a BTL-level decision, no a
>> special path in the PML.
>> Is there a reason IPC support cannot be hidden down in the SMCUDA BTL?
>> Thanks,
>> George.
>> On Aug 21, 2013, at 23:00 , svn-commit-mailer_at_[hidden] wrote:
>>> Author: rolfv (Rolf Vandevaart)
>>> Date: 2013-08-21 17:00:09 EDT (Wed, 21 Aug 2013) New Revision: 29055
>>> URL:
>>> Log:
>>> Fix support in smcuda btl so it does not blow up when there is no CUDA IPC
>> support between two GPUs. Also make it so CUDA IPC support is added
>> dynamically.
>>> Fixes ticket 3531.
>>> Added:
>>> trunk/ompi/mca/btl/smcuda/README
>>> Text files modified:
>>> trunk/ompi/mca/btl/btl.h | 2
>>> trunk/ompi/mca/btl/smcuda/README | 113
>> ++++++++++++++++++++++
>>> trunk/ompi/mca/btl/smcuda/btl_smcuda.c | 104
>> ++++++++++++++++++++
>>> trunk/ompi/mca/btl/smcuda/btl_smcuda.h | 28 +++++
>>> trunk/ompi/mca/btl/smcuda/btl_smcuda_component.c | 200
>> +++++++++++++++++++++++++++++++++++++++
>>> trunk/ompi/mca/btl/smcuda/btl_smcuda_endpoint.h | 5 +
>>> trunk/ompi/mca/common/cuda/common_cuda.c | 29 +++++
>>> trunk/ompi/mca/common/cuda/common_cuda.h | 3
>>> trunk/ompi/mca/pml/ob1/pml_ob1.c | 11 ++
>>> trunk/ompi/mca/pml/ob1/pml_ob1_cuda.c | 42 ++++++++
>>> trunk/ompi/mca/pml/ob1/pml_ob1_recvreq.c | 6
>>> 11 files changed, 535 insertions(+), 8 deletions(-)
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