From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rich Martin Date: Sun, 26 Jul 1998 00:45:53 +0000 Subject: Re: Ultra AXmp Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ultralinux@vger.kernel.org I'm not sure this dicussion belongs on this list, but I'll provide an alternate opinion to liven the debate. > It has been hard to communicate computer scientists (:-) since most of them > do not understand what PDE stands for. ;-) To put it in short, the difficulty Yup! All we get from the scientists is something like "please solve my Ax=b fast. Oh yea, I have a some funny structure in my A and b too". > numerical problems are not in that category. Searching for low-latency, > high-throughput inter-processor communication should be still listed high > on our agenda. At least this is my view. Actually, anything that can be expressed in terms of large linear algebra operations is a good candidate for a Beowulf style system. There has been endless work on MPPs and recently, clusters in this area. Now there are plenty of good latency tolerating algorithms for most common operations. Dissecting the NAS Parallel Benchmarks on our cluster has convinced me that these codes can run over a high bandwidth TCP just fine. On our 64 node UltraSparc/Myrinet cluster, most of the NPB codes spent 5%-15% of the time in communication. FT (a 3D FFT), the program that stresses the network the most, is just a bandwidth hog (high bandwidth alone is not an interesting CS problem). FT, like all the other NPB codes, can tolerate huge software overheads and network latencies. Hardly worth investing time or $$$ in a communication network when you're only spending 15% of the time there! If the NPB aren't representative, well, that's another problem ... I'm more and more convinced that inter-processor communication is no longer a first order issue. Focusing on memory system efficiency (effective use of the cache and memory BW) will get you much more bang for your buck. Even in the parallel case, I would spend money on huge L2 caches and memory bandwidth over processor interconnect. My humble $0.02 worth... -Rich