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Subject: Re: [OMPI devel] Threshold for pinning down user-buffers
From: Nathan Hjelm (hjelmn_at_[hidden])
Date: 2014-05-27 10:40:52


This limit is controlled by several MCA variables. Contiguous segments
larger than the btl_openib_eager_limit will use the RDMA protocol (Get) if
mpi_leave_pinned is set and the RDMA RNDV (Put) protocol
otherwise. Both of these protocol pin the user buffer on both sides.

-Nathan

On Fri, May 23, 2014 at 04:39:36PM -0500, Siddhartha Jana wrote:
> Hi,
> Is my understanding correct?
> While servicing MPI_Send using eager protocol over openib, there is a
> data-size threshold below which it is preferred to copy the contents of
> the user-buffer to a pre-pinned buffer instead of directly pinning down
> the user-buffer. If this is correct, how does one determine this
> threshold?
> As always, thanks for the help
> Sid

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