Multi-core, I lie awake at night thinking about this stuff. There seem to be no quick answers.
The thing that amazes me about multi-core is how many people consider the performance of a single process to be a good measure of total processor performance. If you are going to by a quad-core CPU to run one process at a time, then this is good test otherwise it is like predicting performance of your code on cluster by running it on the head node as single serial job. Over the past 8-10 months I have had the chance to test Intel quad-core, AMD dual core (soon I'll have some Barcelona's) and here are my conclusions. The details of what I found are in my columns in Linux Magazine, which is slowly making its way to the LM web site (and eventually ClusterMonkey): - how well multiple processes run (use memory) on quad-core is very application specific. I have a simple test script that calculates what I call "effective cores". I have seen these results range from about 2-7 on a dual socket quad-core Intel system (8 cores total) and a quad socket dual core AMD system (8 cores total). - running a single copy of the NAS FT benchmark on a clovertown was much faster than a comparable Opteron. But, running a parallel MPI version of FT on 8 cores showed the AMD system to be faster. - on Intel quad-cores where the process is placed can have large effect on performance. This is largely due to the fact that you have four dual core woodcrests each with it's own cache. Naturally, if you have four processes running it is best if each one gets its own woodcrest. To the OS the all look the same. Other than Intel MPI, I don't know of any other MPI that attempts to optimize this. Open MPI has some processor affinity but it is not all that sophisticated (yet). - again depending on the application, GigE may not sufficient to support the amount of traffic that multi-core can generate. So if your code ran well on GigE, it may not on a multi-core cluster. Things like IB or Myrinet 10GigE may be needed. Please note, I am not trying to pick a winner, were that even possible. I want to state that more than ever testing your code(s) in parallel on these systems is critical if you want to get optimal performance. One other thing I found as well. I recently ran the NAS parallel benchmarks on a dual socket quad core Intel system (8 cores total) using both the OpenMP (GNU 4.2) and MPI (LAM) libraries. Anyone want to guess what produced the best results? -- Doug > Hi everybody, > > As you may be aware of, Intel has reduced the price of its Quad CPUs, > dramatically. > > Does anyone have any experience using Intel Quad-Core CPUs in a Beowulf > Cluster? > > Do you prefer these ones over AMD Opteron? > > Essentially, are Intel Quad CPUs having really FOUR cores? Are they really > 64-bit processors, as Opterons are? > > Thanks for any comment on each of my questions. > > Wishes, > rmb > > > -- > Best, > Ruhollah Moussavi Baygi > > > !DSPAM:46cc246327668298414181! > _______________________________________________ > Beowulf mailing list, Beowulf@beowulf.org > To change your subscription (digest mode or unsubscribe) visit > http://www.beowulf.org/mailman/listinfo/beowulf > > > !DSPAM:46cc246327668298414181! > -- Doug _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
