RE: [myrinet] Re: Question on max sizes

> > I was just wondering if there is a limit to the maximum amount of data
that
> > you can send in one hit across the myrinet.

GM happens to divide messages into 4k parts, but it can send arbitrarily
long messages, and doesn't suffer much performance loss for having divided
the packets except for sizes just over 4k and 8k. Other people have
mentioned what other drivers might be able to do.

> > Any limit (non-physical) on the amount of DMA that can be contigously
> > allocated?

GM doesn't use contiguous physical memory for DMA. It uses contiguous
virtual pages, which means that contiguity isn't a limit (is it even a
word?) The limit is how much memory your OS will let you pin. (GM's DMA
routines essentially do a series of page-size transfers, so they zig-zag to
follow the pages through memory.)

-- g