Slashdot Mirror
The Impact of Memory Latency Explored
EconolineCrush writes "Memory module manufacturers have been pushing high-end DIMMs for a while now, complete with fancy heat spreaders and claims of better performance through lower memory latencies. Lowering memory latencies is a good thing, of course, but low-latency modules typically cost twice as much as standard DIMMs. The Tech Report has explored the performance benefits of low-latency memory modules, and the results are enlightening. They could even save you some money."
Beware, one of the banner advertiser on that page (netshelter.net) is trying to buffer overflow with strangely crafted cookie. Hope you do not run your Firefox on Windows...
There you are, staring at me again.
ExtremeTech Article
Sorry, I call BS on your entire post. The difference in latencies here is miniscule -- it's not like we're talking about having the CPU wait 2 clock cycles vs 30 clock cycles. It's closer to 13 vs 25 (not exact, but the magnitude of difference is close). That just doesn't matter that much -- the reality is that if you have a cache miss then you're looking at 20-30 cycles (or, more likely, 40-60 cycles) of stall while you fetch the data from main memory.
The kind of changes you're talking about require vastly faster memory. Not the kind of latency differences being discussed here at all. Both of these are "high latency" compared to what would be needed for your theoretical redesign of the entire software stack. And even then, you just become utterly and completely screwed if you have to hit virtual memory, possibly more so than you are now because you've re-orchestrated everything around the idea that latency is a non issue.
Oh, and latency is getting worse, not better, and has been for a long, long time. CPU speeds long ago outstripped the speeds of our fastest memory (well, fastest while still not costing absurd amounts of money...), and the newer memory formats (DDR, DDR2, DDR3, RDRAM, etc) have higher latencies in exchange for greater bandwidth.
Have to agree with AC on the cpu issue, taken from the http://techreport.com/reviews/2005q2/athlon64-x2/i ndex.x?pg=16
Conclusions
Let's start by talking about the Athlon 64 X2 4200+. This CPU generally offers better performance than its direct competitor from Intel, the Pentium D 840. Most notably, the X2 4200+ doesn't share the Pentium D's relatively weak performance in single-threaded tasks like our 3D gaming benchmarks. The Athlon 64 X2 4200+ also consumes less power, at the system level, than the Pentium D 840--just a little bit at idle (even without Cool'n'Quiet) but over 100W under load. That's a very potent combo, all told.
In fact, the X2 4200+ frequently outperforms the Pentium Extreme Edition 840, which costs nearly twice as much. Thanks to its dual-core config, the X2 4200+ also embarrasses some expensive single-core processors, like the Athlon 64 FX-55 and the Pentium 4 Extreme Edition 3.73GHz. Personally, I don't think there's any reason to pay any more for a CPU than the $531 that AMD will be asking for the Athlon 64 X2 4200+.
If you must pay more for some reason, the Athlon 64 X2 4800+ will give you the best all-around performance we've ever seen from a "single" CPU. The X2 4800+ beats out the Pentium Extreme Edition 840 virtually across the board, even in tests that use four threads to take best advantage of the Extreme Edition 840's Hyper-Threading capabilities. The difference becomes even more pronounced in single-threaded applications, including games, where the Pentium XE 840 is near the bottom of the pack and the X2 4800+ is constantly near the top. The X2 4800+ also consumes considerably less power, both at idle and under load.
The X2 4800+ gives up 200MHz to its fastest single-core competitor, the Athlon 64 FX-55, but gains most of the performance back in single-threaded apps thanks to AMD's latest round of core enhancements, included in the X2 chips. The X2 4800+ also matches the Opteron 152 in many cases thanks to Socket 939's faster memory subsystem. Remarkably, our test system consumes the same amount of power under load with an X2 4800+ in its socket as it does with an Athlon 64 FX-55, even though the X2 is running two rendering threads and doing nearly twice the work. Amazing.
There's not much to complain about here, but that won't stop me from trying. I would like to see AMD extend the X2 line down two more notches by offering a couple of Athlon 64 X2 variants at 2GHz clock speeds and lower prices. I realize that by asking for this, I may sound like a bit of a freeloader or something, but hey--Intel's doing it. No, the performance picture for Intel's dual-core chips isn't quite so rosy, but the lower-end Pentium D models will make the sometimes-substantial benefits of dual-core CPU technology more widely accessible. If AMD doesn't follow suit, lots of folks will be forced to choose between one fast AMD core or two relatively slower Intel cores. I'm not so sure I won't end up recommending the latter more often than the former.
Beyond that, the giant question looming over the Athlon 64 X2 is about availability, as in, "When can I get one?" Let's hope the answer is sooner rather than later, because these things are sweet.
Sig