Author: Jeremiah Penery
Date: 15:31:30 08/27/03
Go up one level in this thread
On August 27, 2003 at 17:17:39, Robert Hyatt wrote: >On August 26, 2003 at 18:38:34, Jeremiah Penery wrote: > >>On August 26, 2003 at 11:42:03, Robert Hyatt wrote: >> >>>On August 26, 2003 at 03:00:52, Johan de Koning wrote: >>> >>>>On August 25, 2003 at 18:04:29, Robert Hyatt wrote: >>>> >>>>>A single cpu that will run crafty at 1M nps has a cache-cache and cache-memory >>>>>bandwidth of X bytes/second. A single cpu that runs crafty at 2M nps has >>>>>exactly twice the cache-cache and cache-memory bandwidth and twice the clock >>>>>frequency. A dual-cpu just needs two cpus, but the two cpus give twice the >>>>>cache-cache bandwidth, but _no_ improvement in cache-memory bandwidth. >>>> >>>>Nope, C2M bandwith is constant, regardless of n and f (hence constant :-). >>> >>>Actually it isn't. Some duals use interleaving. Some don't. All quads I >>>have here use 4-way interleaving to ramp up the bandwidth significantly. >>> >>>All machines are _not_ created equal... >> >>A great many single-CPU motherboards you can buy offer dual-channel memory >>and/or 4-way memory interleaving. > >1. I don't know much about dual-channel, but it doesn't sound related to >interleaving. It doubles available memory bandwidth. Not by trickery, but by actually having two full-width memory channels. Much like interleaving, it requires paired DIMMs to accomplish. >2. I have looked at most every single-cpu machine we have here and they >are _all_ plain memory boxes (non-interleaved). The easiest way to catch >interleaving is to find a requirement that you add two (or four) DIMMS, one >per "bank". If you have just one DIMM, or you have just one/two/three DIMM >slots, that MB isn't interleaving. I didn't say Dell sold single-cpu machines that had interleaving. But every motherboard that any of my friends or I have bought in the last few years offers 4-way memory interleaving. Yeah, you can't turn it on unless you have 2+ DIMMs installed, but it's still there. >> I don't know if many of the SMP (2-CPU, >>specifically) boards for Intel or Athlon have that stuff or not. Opteron >>doesn't worry about it, as each CPU has its own dedicated (dual-channel) memory, >>and N CPUs have N times the aggregate bandwidth of a single-CPU machine. > > >Yes, but Opteron is NUMA, which has its _own_ problem issues to deal with. I don't see why NUMA should pose any problems. It's all handled by the hardware and the operating system anyway. >Anytime you say "each processor has its own memory" you are talking NUMA. Yes, I know that. >I haven't seen any recent Intel MBs that didn't have interleaving. If you >don't do that, you take a big performance hit as memory has a hard enough >time keeping up with one cpu, much less two, without some sort of bandwidth >increasing trickery. >All of my quads have 4-way interleaving without exception, going back to my >original quad pentium-pro 200 box I still have (ALR Revolution). And all of my friends' and my single-cpu boxes have 4-way interleaving also.
This page took 0.05 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.