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#1
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster
than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? J. |
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#2
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. Because it is in practical situations. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. Thats not the situation where a dual core processor is theoretically faster. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? No, just looking at the wrong situation. |
#3
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. Because it is in practical situations. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. Thats not the situation where a dual core processor is theoretically faster. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? No, just looking at the wrong situation. |
#4
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
Its not a case of right or wrong - A single CPU core will be faster, but only in certain circumstances (non hyperthreading apps as you say) But its the OS that uses the cores and not necessarily the program. If you have a multi core CPU most of the windows tasks are being handled between the cores, so the load is much less than a single core CPU You are basing your ideas on just the program and not the OS and nearly all Core2Duo CPUs have more Cache than their single core comparisons -- Dalo Harkin Posted via http://www.computerhelpforums.net |
#5
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
Its not a case of right or wrong - A single CPU core will be faster, but only in certain circumstances (non hyperthreading apps as you say) But its the OS that uses the cores and not necessarily the program. If you have a multi core CPU most of the windows tasks are being handled between the cores, so the load is much less than a single core CPU You are basing your ideas on just the program and not the OS and nearly all Core2Duo CPUs have more Cache than their single core comparisons -- Dalo Harkin Posted via http://www.computerhelpforums.net |
#6
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Should Core 2 Duo CPU not be theoretically slower than singlecore with double MHz?
Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? J. As you've already noted, the gain in moving a workload from a monoprocessor to a multiprocessor depends on the workload. Doh. Some workloads will gain nothing, while some will scale almost linearly (up to some maximum number of processors). I do have some experience in constructing workloads to show how wonderful multiprocessors a when one of my artificial workloads ran on a monoprocessor, the OS reported that the app got 100% of CPU time; when it ran on a dual-processor, the OS reported that the app (fully decomposed by hand) got 205% of CPU time. Amazing, eh? My father would say: "Benchmarks don't lie, but liars do benchmark". -- Cheers, Bob |
#7
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Should Core 2 Duo CPU not be theoretically slower than singlecore with double MHz?
Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? J. As you've already noted, the gain in moving a workload from a monoprocessor to a multiprocessor depends on the workload. Doh. Some workloads will gain nothing, while some will scale almost linearly (up to some maximum number of processors). I do have some experience in constructing workloads to show how wonderful multiprocessors a when one of my artificial workloads ran on a monoprocessor, the OS reported that the app got 100% of CPU time; when it ran on a dual-processor, the OS reported that the app (fully decomposed by hand) got 205% of CPU time. Amazing, eh? My father would say: "Benchmarks don't lie, but liars do benchmark". -- Cheers, Bob |
#8
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Should Core 2 Duo CPU not be theoretically slower than singlecore with double MHz?
On May 21, 7:57*am, (Jason Stacy) wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? J. I think the real world answer may be that many applications do require data to and from a hard drive. Any time waiting for this will slow the process down. Thus most applications will become multi-threaded. Also, although the processor speed may be so and GHz (nb most CPUs run at GHz speed these days rather than MHz speed), the different levels of cache memory are slower . Have you done any actual tests to see which is fastest? Michael |
#9
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Should Core 2 Duo CPU not be theoretically slower than singlecore with double MHz?
On May 21, 7:57*am, (Jason Stacy) wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? J. I think the real world answer may be that many applications do require data to and from a hard drive. Any time waiting for this will slow the process down. Thus most applications will become multi-threaded. Also, although the processor speed may be so and GHz (nb most CPUs run at GHz speed these days rather than MHz speed), the different levels of cache memory are slower . Have you done any actual tests to see which is fastest? Michael |
#10
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
In comp.sys.ibm.pc.hardware.storage Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Well, it depends highly on the workload. For a non-paralellizable workload (which is surprinsingly common), the 2-core is only 50% as fast and nothing at all can be done about it. For a very well paralellizable workload, it benefits from two caches instead of one. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? No. You have it exactly right. Arno |
#11
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
In comp.sys.ibm.pc.hardware.storage Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Well, it depends highly on the workload. For a non-paralellizable workload (which is surprinsingly common), the 2-core is only 50% as fast and nothing at all can be done about it. For a very well paralellizable workload, it benefits from two caches instead of one. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? No. You have it exactly right. Arno |
#12
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
"Jason Stacy" wrote in message ... I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? J. The 1.7GHz Core 2 Duo running single core will be slower than a 3.4GHz P4. On the other hand, a 2.4GHz Core 2 Duo on single core will beat the 3.4GHz P4. It's because the Core 2 processes more instructions per clock cycle than a P4, but the ratio is less than 2:1. Being multithreaded does not automatically enable an application to use more than one core. The application must be coded to utilize multiprocessors. Most applications are multithreaded, but few can fully utilize more than one core. If you look in the Processes tab of Task Manager you can see how many threads an application uses. |
#13
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
"Jason Stacy" wrote in message ... I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster than a single core with 3.4 MHz. I am NOT talking about additional features like Pipeling and Hyperthreading but the core fact that the power is split over two cores. Assume the following situation: A NON-THREADED application needs as much CPU power as possible for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power (remaining 1 % are for system services). When I run the same application on a two core system then it can occupy only ONE of the two cores with 1.7 MHz. Because it is non-threaded it cannot request the other core as well. So it must be slower (given all other side-conditions are equal). Am I wrong? J. The 1.7GHz Core 2 Duo running single core will be slower than a 3.4GHz P4. On the other hand, a 2.4GHz Core 2 Duo on single core will beat the 3.4GHz P4. It's because the Core 2 processes more instructions per clock cycle than a P4, but the ratio is less than 2:1. Being multithreaded does not automatically enable an application to use more than one core. The application must be coded to utilize multiprocessors. Most applications are multithreaded, but few can fully utilize more than one core. If you look in the Processes tab of Task Manager you can see how many threads an application uses. |
#14
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
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#15
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Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?
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