Eugene Loh wrote:
In mca_btl_sm_get_sync(), I see this:
/* Use the DMA flag if knem supports it *and* the segment length
is greater than the cutoff. Note that if the knem_dma_min
value is 0 (i.e., the MCA param was set to 0), the segment size
will never be larger than it, so DMA will never be used. */
icopy.flags = 0;
if (mca_btl_sm_component.knem_dma_min <= dst->seg_len) {
icopy.flags = mca_btl_sm_component.knem_dma_flag;
}
I'm going to poke around some more, but this doesn't on the surface
make sense to me. If knem_dma_min==0, it would seem as though the
segment size will *always* be at least that large and DMA will
*always* be used (if supported).
Answering my own question (or guessing, in any case), maybe the code is
okay but the comment is misleading. If knem_dma_min==0, then
mca_btl_sm_component_init() sets knem_dma_flag to 0. So, the seg_len
test passes, but it has no effect.