On Thu, 2006-02-09 at 16:37 -0700, Brightwell, Ronald wrote: > I apologize if it seems like I'm picking on you. No offense taken.
> I'm hypersensitive to > people trying to make judgements based on micro-benchmark performance. > I've been trying to make an argument that two-node ping-pong latency > comparisons really only have meaning in the context of a whole system. It's very clear to me that micro-benchmarks do not tell you very much about real application behaviour; that's not the question. They are nevertheless relevant to me because, right or wrong, people who buy stuff look at them. And I work for a commercial outfit. I may sound silly saying that, but they might be right to look at it, they just need to look at the rest too. A micro-benchmarks tells you how much you have of a given currency, that you can trade for another. It tells you something about the implementation; how efficient the code is, how well the hardware is utilized, etc. Not in every respect, but some. It also tells you how far you can emphasize a given feature at the expense of all others, if it happens that at some point in time it is what you most need. By making the argument that a particular characteristic is irrelevant, you are essentially making a hard coded tradeoff, rather than letting the users do it. Back to the specific issue of latency vs. scale. Okay for CG and FT, the cross-over may be <32, but that's not for all the cases and the difference visible at 32 is pretty small. So, it is application dependent, no question about it, but small-msg rdma is beneficial below a given (application-dependent) cluster size. -- Jean-Christophe Hugly <j...@pantasys.com> PANTA
