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#1
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Macro-Op fusion does not work in 64-bit mode
"The thing is though, while MOF may be touted as the best thing since
sliced bread, it does not cause many performance problems when it is off. It appears that the bottleneck in the CPU is not in that aspect of the pipeline, so its loss has little speed impact. More on this when the testing is complete." http://www.theinquirer.net/default.aspx?article=33347 Macro-op Fusion was one of the big hype items of the Conroe/Merom/Woodcrest. This feature is supposed to be one of the things giving Intel it's edge over AMD in the performance wars. Now it turns out that it doesn't even work in 64-bit mode. But apparently it's no big deal. Most of us have already figured out that the real secret behind CMW is its big L2 cache, but Intel downplayed that. So Intel can't have it both ways, either MOF is important, and Intel will have to explain why it isn't available when in 64-bit mode and why CMW is crippled in that mode? Or MOF isn't important, and Intel has to admit that it's all due the cache. Yousuf Khan |
#2
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Macro-Op fusion does not work in 64-bit mode
On 31 Jul 2006 16:38:07 -0700, "YKhan" wrote:
and Intel has to admit that it's all due the cache. Is it really just the cache and nothing else? :P -- A Lost Angel, fallen from heaven Lost in dreams, Lost in aspirations, Lost to the world, Lost to myself |
#3
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Macro-Op fusion does not work in 64-bit mode
On 31 Jul 2006 16:38:07 -0700, "YKhan" wrote:
"The thing is though, while MOF may be touted as the best thing since sliced bread, it does not cause many performance problems when it is off. It appears that the bottleneck in the CPU is not in that aspect of the pipeline, so its loss has little speed impact. More on this when the testing is complete." http://www.theinquirer.net/default.aspx?article=33347 Macro-op Fusion was one of the big hype items of the Conroe/Merom/Woodcrest. This feature is supposed to be one of the things giving Intel it's edge over AMD in the performance wars. Now it turns out that it doesn't even work in 64-bit mode. But apparently it's no big deal. Most of us have already figured out that the real secret behind CMW is its big L2 cache, but Intel downplayed that. So Intel Actually I've been rather adamant that there are a LOT of factors that are affecting performance in the Core architecture. Sure, the extra cache helps. Faster bus speed helps too, and more pipelines, better decoders, an excellent brand predictor, improved TLB and hey, even Macro-Op Fusion, just to name a few. Take away any one of these and you are going to lose some performance. Going from 4MB to 2MB of cache costs about 3.5% performance (see: http://www.anandtech.com/cpuchipsets...spx?i=2795&p=4 ), while 1MB or L2 would probably drop performance further. Substantial yes, but not nearly enough to make up for the improvements vs. either the Athlon64 X2 or the Core Duo (Yonah) chips before it. can't have it both ways, either MOF is important, and Intel will have to explain why it isn't available when in 64-bit mode and why CMW is crippled in that mode? Or MOF isn't important, and Intel has to admit that it's all due the cache. Or they just tell the truth that Macro-Op Fusion is just one of many features that helps performance. It's also supposed to reduce power consumption slightly. In all it's damn near impossible to predict just how much the loss of this one feature will really change things though, since there are many other variables that come into play here. ------------- Tony Hill hilla underscore 20 at yahoo dot ca |
#4
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Macro-Op fusion does not work in 64-bit mode
"YKhan" wrote in message oups.com... "The thing is though, while MOF may be touted as the best thing since sliced bread, it does not cause many performance problems when it is off. It appears that the bottleneck in the CPU is not in that aspect of the pipeline, so its loss has little speed impact. More on this when the testing is complete." http://www.theinquirer.net/default.aspx?article=33347 Macro-op Fusion was one of the big hype items of the Conroe/Merom/Woodcrest. This feature is supposed to be one of the things giving Intel it's edge over AMD in the performance wars. Now it turns out that it doesn't even work in 64-bit mode. But apparently it's no big deal. Most of us have already figured out that the real secret behind CMW is its big L2 cache, but Intel downplayed that. So Intel can't have it both ways, either MOF is important, and Intel will have to explain why it isn't available when in 64-bit mode and why CMW is crippled in that mode? Or MOF isn't important, and Intel has to admit that it's all due the cache. Yousuf Khan If you actually looked at the benchmarks, you would realize that the improved performance cannot be attributed to the cache alone. |
#5
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Macro-Op fusion does not work in 64-bit mode
The little lost angel wrote:
On 31 Jul 2006 16:38:07 -0700, "YKhan" wrote: and Intel has to admit that it's all due the cache. Is it really just the cache and nothing else? :P Well, it might also be the predictive algorithms for populating the cache, but that's really part of the cache. Yousuf Khan |
#6
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Macro-Op fusion does not work in 64-bit mode
Mark wrote:
If you actually looked at the benchmarks, you would realize that the improved performance cannot be attributed to the cache alone. The cache is 4 times bigger than anything AMD has. What else would it be? We've already shown it's not macro-op fusion. Yousuf Khan |
#7
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Macro-Op fusion does not work in 64-bit mode
Yousuf Khan wrote:
Well, it might also be the predictive algorithms for populating the cache, but that's really part of the cache. What about other things like the out of order load/store? That's memory and not cache. It seems that every thing just adds a small % thus adding up. While individually, the large cache or whatever does not appear to be the "key" component. |
#8
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Macro-Op fusion does not work in 64-bit mode
On Sun, 06 Aug 2006 11:49:27 +0800, Seraphim wrote:
Yousuf Khan wrote: Well, it might also be the predictive algorithms for populating the cache, but that's really part of the cache. What about other things like the out of order load/store? That's memory and not cache. It seems that every thing just adds a small % thus adding up. While individually, the large cache or whatever does not appear to be the "key" component. The out of order load/store *is* predictive, in particular the disambiguation and was said to include speculative components, without further elucidation by Intel. The large cache is an important part of such a strategy to avoid/minimize negative effects. It's quite rare for microarchitecture tweaks like op-fusion, or additional pipeline paths to yield benefits which are consistently measurable. I *do* wish that the benchmarkers would quit quoting "latency" performance using a program which is now clearly insufficient for the job. -- Rgds, George Macdonald |
#9
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Macro-Op fusion does not work in 64-bit mode
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#10
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Macro-Op fusion does not work in 64-bit mode
"Yousuf Khan" wrote in message
... Mark wrote: If you actually looked at the benchmarks, you would realize that the improved performance cannot be attributed to the cache alone. The cache is 4 times bigger than anything AMD has. What else would it be? We've already shown it's not macro-op fusion. Yousuf Khan How much impact would something like a wider execution path make? This is coming from someone who is more of a layman than anything else when it comes to the specifics of how CPU's actually perform their duties, so I'm asking out of curiosity. Having read an analysis off of the anandtech website, one of the key architectural changes they point out is how much wider the Core 2 is compared to a PIII/P4/Ahtlon64. Core 2, for instance, is the only core among those that can execute 128bit SSE instructions in a single cycle. Is this the type of thing that might add up to create a real impact? Carlo |
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