RGB, I look forward to buying you a beer :-) Hmmm, Dopple Bock. Unfortunately Christmas will be in CA this year, not NC, on account of my nephews new baby. (Of course it's a good thing in other ways :-) I'm thinking, it might be fun to have say 4 cheapo 1.5GHz nodes and say 1 3GHz with two cores and let them compete. My algorithm wants to referee. (My algorithms talk to me.) Your points about the L2 and the 32-bit-ness give me pause. I maybe don't want to saddle myself with 32 bit things that won't play well with near-future 64 bit things, but OTOH it's cheap to look see. Thanks, Peter
On Nov 8, 2007 1:39 PM, Robert G. Brown <[EMAIL PROTECTED]> wrote: > > On Thu, 8 Nov 2007, Peter St. John wrote: > > > Recently, probably you noticed, Walmart began selling a $200 linux PC. > > (Apparently the OS is just Ubuntu 7.10 with a small xindow manager > > instead of Gnome or KDE). Now Slashdot points to > > http://www.linuxdevices.com/news/NS5305482907.html, the MB being sold > > separately for $60 ("development board"). It has 1.5GHz CPU, > > unpopulated memory (slots for 2GB), one 10/100 connection. Does this > > look to y'all like fair FLOPS/$ for a kitchen project? I'm thinking 6 > > of them as compute nodes per 8 port router, with a bigger head node > > for fileserving. (actually I'll use a spare room but you know what I > > mean). An arrangement like this might be faster RAM access per core, > > compared to multicore, since each core has no competition for is't own > > memory, right? > > Well by now you surely have heard the YMMV litany enough times not to > hear it again from me, but YMMV quite a bit here so let me indicate a > few potential difficulties. > > a) For this money, I'm guessing the CPU is a 32 bit Celery, which has a > very small L2. For some code this won't matter, but if you're worrying > about multiple cores and a memory bottleneck, let me assure you the L2 > bottleneck on a single 32-bit channel will likely be much worse. > > b) Amdahl's law rewards higher clock and fewer CPUs over lower clock > and more CPUs almost (but not quite) without exception. I doubt that > you are an exception. > > c) A 64-bit CPU has some superlinear speedup compared to a 32-bit CPU > at constant clock, for memory bound code especially. 64-bit CPUs have > much larger caches as well. This CAN work against you for very cache > unfriendly code, but again in 99% of all applications it will work for > you -- it is what a cache "does". > > d) A perfectly fair question is to what extent the memory bus is > oversubscribed on a 64-bit dual core, say, a very cheap AMD-64 at > roughly twice the clock, with more than twice the total memory > bandwidth, and with two cores. This is the question that depends in > detail on YOUR APPLICATION. Many applications are de facto CPU bound > and you get clock speed scaling within a CPU family all the way down to > small cache Celerons. Others are vehemently not. "YMMV", so you have > to analyze YOUR application to figure out which it is, where the easiest > way by far to find out is to just try it. > > Sounds like it will cost you somewhere between $100 and $200 to set up a > minimal system -- cheap case/power, motherboard, memory, a borrowed > video card. You can probably beg, borrow, or buy a dual core AMD at > some middling low (but much higher!) clock for no more than $400. Run > your presumably EP application on the one, and on the other two at a > time. Buy lots of the winner, use the loser as a desktop or head node > (even the Celery should be fine for that, especially on a 100 Mbps > network). > > Now, I'm a gambling man (as you may not know) and I will bet you one > bottle, can, or glass of ice-cold or cellar cool clean and refreshing or > thick and chewy beer as the winner prefers, to be delivered at a > mutually convenient time (such as both of us sitting side by side at in > a venue that purveys said beverages), that the medium-low end AMD-64 > kicks the ass of the maximally cheap Celery in price-performance on your > application (where I have an unfair advantage in that I know something > about your application, but I'd make the same bet if I didn't). > > To go into detail, I expect that at contant cost you'll end up with > somewhere in the ballpark of 2-3x aggregate bogomips/$ from the AMD, > that memory bottlenecks will eat up no more than a small part of it (I > actually expect the AMDs to win here TOO because of the probably at > least doubled total memory bandwidth and larger cache), that when you > factor in a roughly 4x increase in required system volume and 3x > increase in total power consumption required to run the same number of > Celeries that will match the AMD, at a marginal cost of roughly > $200/year in increased power costs and some increased investment of your > "free" time to install and mange the extra systems... well, let's just > say that I think that the Celeries will look ugly. And I'd expect > similar savings from the lowball dual core Xeons, honesly -- system > price around $350-500 stripped to match where you vary in this range to > find the sweet spot in terms of total memory, processor clock, and other > configuration details. > > Before you turn me down, note that this is a win-win bet for both of us, > since the winner gets to buy the next round...;-) > > rgb > > > Thanks, > > Peter > > _______________________________________________ > > Beowulf mailing list, Beowulf@beowulf.org > > To change your subscription (digest mode or unsubscribe) visit > > http://www.beowulf.org/mailman/listinfo/beowulf > > > > -- > Robert G. Brown > Duke University Dept. of Physics, Box 90305 > Durham, N.C. 27708-0305 > Phone(cell): 1-919-280-8443 > Web: http://www.phy.duke.edu/~rgb > Lulu Bookstore: http://stores.lulu.com/store.php?fAcctID=877977 > _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
